Explain how the Thief Rogue's Use Magic Device isn't overpowered

Question

I've been looking at the Rogue class lately, and although the Arcane Trickster archetype is really interesting, the Thief archetype, which is the only class to get Use Magic Device, seems also very good, just for this feature. However, scouring around for guides, I see that usually Use Magic Device is never identified as one of the Thief's best features, and features like Fast Hands and taking two turns at the start of combat are deemed more useful.

Why is that? I would expect that with Use Magic Device, the Thief essentially becomes a sneak attacking Clericzard just spamming all kinds of scrolls/wands every other turn, but most don't really consider this feature as the core of the class.

Answer 1

Because obtaining magic items isn’t up to the thief.

The power and flexibility of the Use Magic Device feature is entirely up to the DM. If the DM doesn’t give many (or any) useful items that the thief can take advantage of, then Use Magic Device is not going to be a particularly interesting feature. Use Magic Device is not overpowered because the player can’t even decide if they will be able to use it.

This is outlined in the first chapter of the Dungeon Master's Guide, "Magic in Your World":

Some D&D settings have more magic in them than others. On Athas, the harsh world of the Dark Sun setting, arcane magic is a hated practice that can drain life from the world. Much of Athas’s magic lies in the hands of evildoers. Conversely, in the world of Eberron, magic is as commonplace as any other commodity. Mercantile houses sell magic items and services to anyone who can afford them. People purchase tickets to ride airships and trains propelled by elemental magic.

Consider these questions when fitting magic into your world:

[...]

• How rare are magic items, magical locations, and creatures that have supernatural powers? At what power level do these things go from everyday to exotic?

Then, in Chapter 7: Treasure, in the section "Buying and Selling", we have more guidance that puts magic item commerce well within the DM's purview:

Unless you decide your campaign works otherwise, most magic items are so rare that they aren’t available for purchase. Common items, such as a potion of healing, can be procured from an alchemist, herbalist, or spellcaster. Doing so is rarely as simple as walking into a shop and selecting an item from a shelf. The seller might ask for a service, rather than coin.

[...]

In your campaign, magic items might be prevalent enough that adventurers can buy and sell them with some effort. Magic items might be for sale in bazaars or auction houses in fantastical locations, such as the City of Brass, the planar metropolis of Sigil, or even in more ordinary cities. Sale of magic items might be highly regulated, accompanied by a thriving black market. Artificers might craft items for use by military forces or adventurers, as they do in the world of Eberron. You might also allow characters to craft their own magic items, as discussed in chapter 6.

Answer 2

Casting scrolls with UMD is likely to fail

UMD lets you ignore "all class, race, and level requirements on the use of magic items", but don't forget there are often other requirements for magic items.

You mention spell scrolls, for example they have the following rules:

If the spell is on your class’s spell list, you can read the scroll and cast its spell without providing any material components. Otherwise, the scroll is unintelligible.

The first ruling the DM has to make is whether or not a spell being on a spell list counts as a "class" requirement. I would say it does count, but it's up to your DM of your table.

Sage Advice does say that "The intent is that a Thief can use spell scrolls with Use Magic Device", but whether or not you follow Sage Advice is up to your DM (I personally do not, I just stick to RAW!). This would have been a great opportunity for them to clarify whether it is intended for Thieves to have to roll to use scrolls, but unfortunately it isn't elaborated on.

If they do ok it, you still need to deal with the rest of the rules;

If the spell is on your class’s spell list but of a higher level than you can normally cast, you must make an ability check using your spellcasting ability to determine whether you cast it successfully. The DC equals 10 + the spell’s level. On a failed check, the spell disappears from the scroll with no other effect.

Since thieves have no spells on their list, nor spellcasting ability, they need to make this check to use any scroll. Spamming scrolls of fireball sounds cool, but you need to pass a DC13 every time, and you have a +0 modifier - only a 40% chance of success.

However, even this part is questionable as someone could argue that not having a spell list means you can skip that requirement. Or that the spell list requirement is indirectly a class and level requirement, that it can be skipped. Ask your DM how they rule.

You may never find a magic item you can bypass

So, scrolls are a little sketchy. How about magic items? Many magic items like Necklace of Fireballs or Wand of Polymorph don't have class/race/level requirements. The former has none, the latter requires a spellcaster to attune (again, a DM ruling is required).

There are items like Staff of Power or Holy Avengers which do have requirements you can bypass, but they definitely do not pop up in campaigns often. Unless your DM is benevolent and plentiful with their magic items, you may never see one.

To illustrate how few items fall into this category, I did a search for wands and staffs common to rare and counted up how many at each tier. No common items can be bypassed, 4 uncommon, 5 rare items - and 7 which are questionable. Even if one of these items are found, you are competing with actual spell casters as to who gets to use them.

Also remember you still have to attune the item, using one of your 3 attunement slots.

When it comes to spamming spells, spellcasters do it better

Thieves have great versatility, but actually spellcasters have their own spells so they don't need items. They can also use the same items themselves. If what you want is to spam spells, being a spellcaster will get you there a lot easier.

Answer 3

Excellent answers. I just want to leave this here as a quick perspective

The entire magic item system itself is balanced by several points - attunement slots, uses per day, charge consumption, and rarity. Doing away with class restrictions only bypasses one point of balance (and does so at the cost of an alternative subclass feature). Say you have an uber-powerful Cleric staff. It still only has X charges/day, and you still can't use the item and Sneak Attack in the same turn. You will still only find so many of given rarity, and you can still only attune to three.

Use Magic Device buys you versatility, which is where Rogues are meant to shine, rather than raw power. The other balancing mechanisms ensure that.

Answer 4

Because nine out of ten Rogues will never see it in their campaigns. It comes online at 13th level. Do you know how many campaigns ever go past ten? I can count on one hand the number of games I've played that went past level eight.

Seriously, when it comes to subclasses, you should just ignore everything that comes online later than level six, because the odds of it ever being relevant in more than the very end of your campaign are slim to none.