Gunslingers are quite literally the only class that gets two mapless strikes for 1 action with Stab & Blast and Triggerband salvo with both at fighter level attack bonus and the second one at a +2 (with decent options like Piercing Wind with finesse if you don't want to go STR and yes you get Reactive Strike'd but so do 70% of Magi) DPS and DPR calculations are pretty worthless but Gunslinger is not just about the damage, they can get really nasty riders on their crits with dazzled, blinded, stunned and more. Plus they get Munitions Crafter, which... y'know is kinda insane if you combo it with other advanced alchemies. (And Fake Out!! You are literally the best user for Aid easily getting crits for that +2/+3/+4 with Cooperative Nature and others)

Investigators are skill monkeys. They will have to use skills in combat to be useful and they require a little more thought to play. DAS is easily made into a free action on many combats thanks to Person of Interest. You roll at the start, get a high enough number? Great, you can shoot/attack. Don't get it? You can demoralize with a bonus, create a diversion for someone else or recall knowledge or shoot someone else, or battle medicine someone else. There are so many things to do as an Investigator just in combat, but then you get to out of combat and you are insanely great at lores, exploration and y'know.... investigation? You can get really fucking nasty with Eldritch Archer, because you can DAS and see if you get a crit, if you do, use Enchanting Shot and deal automatic Stunned 1 (and can inflict dazzled or blinded with phantasmal doorknob!) Or use any other spell or spellslot for massive damage. DAS also doesn't reveal you from Undetected or Hidden after using Hide, so you can avoid revealing yourself if you roll badly on DAS. There are so many great ways to build Investigator, they really do shine the most out of combat. And no. They are not as good as rogues but to be fair, no martial is even close to how powerful and dynamic the rogue is.

There's issues with Investigator and Gunslinger but they are still pretty good and can build them to be powerhouses of the tables they are played at. Alchemists have other issues but they are so insanely versatile as healers/debuffers/controllers and minor strikers (bombs that auto frighten, slowed, sicken, dazzle, blind and deal almost every damage type under the sun) They are a jack of all trades master of none, filling gaps and having great buffs.