Mages can achieve much more impressive effects given time to acquire tools and perform ritual casting.
Mages and Direct Damage
Direct damage isn't a Mage's strong suit. There are few Reach options that directly increase damage, so the "more power for more paradox" tradeoff isn't as likely to be available. In most cases, a Mage will do far more damage if they take time to buff up their attacks and then use a mundane weapon, or trap an enemy in a dangerous situation and amplify the hazards.
But let's look at direct damage magic anyway, as it's a simple comparison. Note that Sensory Range (which is only one Reach away) means you completely bypass almost all non-supernatural defences - you have no penalty for Defense, Dodging doesn't help, and even 1 success on the roll means taking your full Potency in damage.
Reaching to take Advanced Scale is relevant, though. It immediately makes a spell more potent - Advanced Scale on a damage spell quadruples the damage output if there are four appropriate targets.
The Power of Gnosis
Increasing spell factors a long way is relatively difficult for a caster with low Gnosis, but it gets significantly easier as Gnosis increases.
The direct addition of Gnosis to dice pools helps - for a fixed target dice pool, every 2 points of Gnosis are worth an extra spell factor. Gnosis also increases the number of Yantras that can be used, from 2 at Gnosis 1 up to 6 at Gnosis 9. The Yantra rules say:
Using such tools grants a bonus to the spellcasting dice pool, up to +5 after penalties
If that "after penalties" is interpreted to include penalties for increasing spell factors, then there's no effective cap on the Yantra dice bonus if you spend all the dice on increasing Spell Factors - if you would exceed +5, just add more penalties instead.
Under this interpretation, a Gnosis 9 mage can trivially add 6 dice for using 6 appropriate 1-die yantras, and could achieve a bonus in the mid-to-high teens if they know the spell as a Rote and have many dots in the linked Skill, and use 2-die Yantras such as High Speech and Runes, and use a strong Shadow Name.
The downside of all this is that Gnosis also significantly increases Paradox risk.
Speaking of Rotes, casting a Rote from a Grimoire or casting a Rote you designed yourself gives your spell the Rote quality, again making it much safer to roll small dice pools - rolling a number of dice with the Rote quality has exactly the same probability of scoring at least 1 success as rolling twice that many dice without. This does require a ritual casting time if using a Grimoire.
Low Gnosis Options
For a low-Gnosis caster, dice pools for spell factors can be increased by using the maximum number of Yantras and picking ones that give large dice bonuses - Rote Mudras and a high Shadow Name merit are best, but High Speech, Material Sympathy and costly or difficult Sacraments, giving 2 dice, are also useful - and casting from a Grimoire, freeing up a few extra dice for the same chance of success from the Rote quality. Combined with Reaches for Advanced Scale and Duration, this can still result in impressive spells.
For example, a Gnosis 2 starting character with a (not particularly impressive!) 3-dot Rote Mudra can, without any Merit spending, achieve a dice pool of Gnosis 2 + Arcanum 3 + Rote 3 + Material Sympathy 2 + Willpower 3 = 13 dice. A 10-dice penalty for +5 Potency would make that 3 dice, which with the Rote Action quality is approximately a 7/8 chance of succeeding, and (assuming Primary Potency) 8 Potency. This does require much more preparation time than shooting someone with a gun; but for the cost of 1 Reach and 1 Mana, a Space 2 character can cast this spell at Sympathetic Range, for (depending on the strength of the connection) between 5 and 8 damage out of nowhere that can't be stopped by any non-supernatural means.
Without the Rote Quality, that same spell at 7 dice, -6 for extra Potency, would hit for 6 damage and an even better chance of success, with no opportunity for the opponent to resist except using supernatural defences or preventing your casting. This does take 2 rounds, but a 1-round cast only loses 2 dice (1 damage) for dropping a Yantra; 5 damage, unaffected by Defense.
Using the maximum number of high-bonus Yantras does mean neglecting your Dedicated Tool, which makes Paradox much more of a concern.
If building for attainable high Spell Factors, prioritise Rotes in Skills you have many dots in and/or a high Shadow Name merit, along with increasing Gnosis and Arcana.
Finally, I'll reiterate: it's also in keeping with the genre's themes for a mage to spend all this time and effort casting similarly potent Fate, Forces, Matter and Mind spells to give themself a Firearms dice pool in the region of 20 with 8-Again, and then just shoot someone with a gun.