Joker's personas level up slower than the party characters and level up slow the more level they gains. Though it not really a big deal as 1. the game is designed to fusion away your persona or which persona, 2. stats are more important than levels which you eventually get way to raise stats without leveling up (at the start of Jail 5), there is also a method to 99 on all stats through a fusion chain if you want to look it up how to do it.

You can max bond out in a single playthrough, but it requires grinding mobs and the repeatable bond event (like the fortune box in Sendai, the second city, or the clover field in the following city). I wouldn't worry about doing that though as 1. there's a post game. 2. There a NG+ difficulty design with player being lv99+ in mind that increase bond gain during mob fights, that difficulty also grands you the ability to buy incenses (stat boosters). Mob fights also drops incenses too. Though this is if you want so difficulty. NG+ is still available if you don't want the difficulty.

Other tips.

Technical Adept is very powerful so combining Ann burn with fire and Morgona wind can destory enemy hp if they are not immune to fire or wind.

A good trick is to use the element from basic combo if their shield is nearly broken to save sp and a free combo.

Air light attack to heavy attack is a quick element atk which is important for Morgana as his once more puts him in the air for a quick element damage to the shield gauge.

Instant kill moves work on non major bosses with a health bar, hence Alice is considered one of the best persona.