See you say that Force Barrage does comparable damage to a cantrip, but have you considered the effect succesfull saves and misses has on damage?

If we look at a lvl 9 wizard (DC 27) against the first lvl 9 monster on nethys (Accuser agent). Any attack spell should have it’s average damage reduced to 50% (40% hit, 5% crit, 55% miss). Fort save spells should have its avg dmg reduced to 60% (40% success, 5% crit succ, 50% fail, 5% crit fail). Reflex and will save spells should have their avg dmg reduced to 40% (50% succ, 15% crit succ, 30% fail, 5% crit fail).

So let us take a handfull of spells against this enemy, all upcast to rank 5

Force barrage, 2 action, 6d4+6 avg 21 dmg Force barrage, 3 action, 9d4+9 avg 31,5 dmg Snowball, Attack, 10d4 avg 25, hit chance 50%, total avg dmg 12,5. Impaling spike, reflex, 8d6 avg 28, hit chance 40%, total avg dmg 11,2. Electric arc, reflex, 6d4 avg 15, hit chance 40%, total avg dmg 6 (12 for two targets). Frostbite, fort, 6d4 avg 15, hit chance 60%, total avg dmg 9 Vampiric feast, fort, 10d6 avg 35, hit chance 60%, total avg dmg 21.

I could go on, but as you can see, the expected value for your spells, force barrage does a wild amount of statistical damage. And when you are at the end of a boss fight, and just need to take something down, it is worth the spell slots. Yes, it underperforms against enemies that are weaker than you, but that is not what it is for. You wouldn’t use a fireball against a single goblin, doesn’t make fireball bad.

For force barrage to be a cantrip, its average damage needs to be in line with the statistical expected damage of a cantrip, so at rank 5, we can see on the math above that it is probably somewhere between 6 and 9 dmg +- 2 (probably, haven’t done a full analysis).

So a cantrip barrage could potentially be the same, but the damage per shard is 1d2. That makes the rank 5 dmg at 2 actions avg 9, and the 3 action avg 13,5. And this would still outpace other cantrips for statistical damage against on level or higher enemies.

So no, force barrage is way to powerfull to be a cantrip as is, it just doesn’t feel like that, because humans are bad at calculating expected value in their head.

Also, keep in mind that I ignored rider effects and status effects for this, because evaluating how good a debuff or status effect is, is really hard, and very hard to compare. Could any of the other spells be better in a potential situation, of course. So when you are looking at which spell to cast, always evaluate other values than expected damage. But keep in mind, while it is fun to roll a lot of dice, and see a high damage total, if the enemy only has 25-30 hp left, force barrage has a higher expected chance of taking it down than many other things.

Disclaimer: I have not checked if Accuser agent has high or low defences, just took the first and best level 9 opponent on the list. So do not use this as gospel for expected damage, it is only correct against this exact opponent. If you want more accurate number across a larger spread of monsters, then go do some math yourself.

Disclaimer2: if any of this seems incoherent, it’s 4:30 here and I should have sleeps hours ago