I think the class should have more of a focus on controlling and debuffing the enemy rather than buffing allies/self. It just doesn't seem to fit with how I picture a mesmerist, especially when a lot of their abilities specialise in enchanting others, yet none of their tricks really do. This way they could even make use of their medium BAB (with the right build/archetype) and do some solo, rogue-style adventures
I think being able to use tricks to give more assorted penalties to opponents would be nice. Confusion, flat-footed, forgetting the mesmerist etc.
I'd house rule that you start with repeating crossbow proficiency (edit: possibly even hand crossbow proficiency, so they can use one something one handed) instead of firearms, and rapid reload instead of gunsmith, as this archetype will mostly be used in worlds without firearms.
Also, you only get a -2 to fire two light crossbows. They count as light weapons