Overall mechanical effects of 16 point buy in 5e

Question

Our DM allows a point buy of ability 16, with a cost of 12. The total cost is still at 27.

I feel this is harmful for balance, because a +1 on your main ability allows reaching a stat of 20 by level 4. It is so good that it practically forces anyone interested in mechanics to either use a +2 main-ability race or take variant human with a +1-main ability feat.

When I mentioned concern about the balance, he said "Don't worry, I will adapt the monsters...". This leads to a red queen effect that punishes those who do not adapt to a max-16 point buy.

I feel that this has a negative effect on the game, because it limits the amount of sensible racial options. I have a strong incentive to take the race with the +2 on the main ability instead of the one whose flair and storytelling possibilities interests me most.

What are the mechanical effects of allowing a point buy max of 16?

A good answer should contain a mathematical / mechanical analysis of how bounded accuracy interacts with this change, under special consideration of the fact that it seems the monsters are buffed to adapt to the higher stat max.

Answer 1

This doesn't actually affect the balance of the game that much, certainly not enough to require that enemy monsters be modified to match.

What this does affect, however, is how you distribute your stats. If you can have a 16 in your main attack stat, you will, almost guaranteed, no matter your class. There's just no really good reason not to do so, if it will give you an advantage. In many cases, classes also have a very important secondary ability score, or at the very least constitution, which they may also want to raise up to 16.

This leaves very few points afterwards to spend on other abilities, leaving character that are extremely good at one or two things, and terrible at everything else. While this might be worth it mechanically, it can negatively affect the game by making each player very specialized in what they do compared to normally.

By restricting ability scores to 15, you encourage a lot more diversity in how your players build their characters. First, as you noted, +2 bonuses to a stat aren't nearly as valuable, since you only need +1 to go from 15 to 16, so +2 just means you can save a few points by starting at 14 instead, and using the 15 for the secondary stat that you have +1 in.

This relieves the pressure to min-max your character, and often leaves you with a few extra point to put into less critical stats, where you're more free to customize your character by, for example, choosing whether your Fighter is an intelligent fighter that uses tactics and knowledge to get and edge, or a wise fighter with an iron will and a natural empathy, or a charismatic fighter that inspires those who follow him.

Answer 2

Compare your stats to the standard array given of 15, 14, 13, 12, 10, 8. This is the standard array given in the book. Even with this, if you take the 15, give a +2 (race), at lv 4, you give it +2, by level 8, you have a 20. From levels 4-8, you have a +1 to hit/damage/AC over that standard array. This is NOT broken. if you have those that pump up one stat over the others, by lv 8, the one's who spread their abilities out will now ALSO have a 20 in a stat, and their other scores will be higher, as they did NOT pay the tax to raise that one ability to a 16 at character creation.

The bottom line goes to this, when you sit down and play with your DM, are you having fun? This can NEVER be answered by math as everyone has different play styles and strengths. I would go ahead and play it out. I've only recently gotten my players to lv 4. They also stole a set of full plate that I didn't expect when there was an army coming in after them. I let them keep it. While it does make our paladin VERY hard to hit for now, I have still been having fun. When the monsters run around the corner and hit from surprise with advantage, an extra +1 to hit/AC/damage isn't very significant.

Answer 3

Thorough Mathematical Analysis of This Situation is Difficult

What you are asking for is an evaluation of unknown "adjusted monsters" against unknown character classes at levels 1-7. We don't know what your GM is planning on doing, he could have a detailed excel spreadsheet where he accurately calculated a need to adjust the early game rules for an expanded standard deviation of expected character abilities, or he may view it as a non-issue and using a small lie to avoid arguing over a minor house rule.

The System Design is Built for Small Numeric Adjustments

Even with bounded accuracy we have to recall that a +1 on a d20 roll is still just a 5% increase. That isn't game changing. Given the system assumes the DM to be responsible to magic item distribution, which can have equitable or even greater impact on the numbers, it can be simply observed that the RAI actively discourage worrying about these things like getting to 20 in your primary stat early.

Stat Spread is Likely to Have a Far Greater Impact on the Game

However it is safe to assume that some, if not most, people WILL max out a stat due to the nature of the game, and in turn this will mean lowering some other stats. Slightly greater strengths, more pronounced weaknesses.

Look at some of the min/max arrays compared to the standard 15, 15, 15, 8, 8, 8:

16, 16, 11, 8, 8, 8

16, 16, 10, 9, 8, 8

16, 15, 13, 9, 8, 8

In pretty much every case what we are really doing is dropping a third stat. Moving from 3 strengths and 3 weaknesses to 2 strengths and 4 weaknesses. Other combinations are possible, but the general idea is that it is enhancing stat spread.

It is more likely for a party as a whole to have a glaring weakness, and (especially if feats are permitted) this is not going to be easily mitigated at later levels. Spending 4 extra points in point-buy to get 1 point stat means 4 less points are put into lower stats which mostly trade on a 1-for-1 basis. Level based stat gains are always a 1-for-1 basis so the long term cost of investing points into a high starting stats is substantial.

In summary

The rule adjustment's biggest impact is probably making the numbers more erratic. And considering failure state for PC's (typically death, or missing crucial information) is far less desirable than failure states for their opponents (Breaking News: Farmer Joe's prize cow returned by friendly adventurers! Sidebar: 800 year old local clan of Kobolds completely eradicated in 8 hour period) one could consider this to be slightly fudging the danger/difficulty upward rather than down.