You don't need items for normal fights, you don't even need items for slime queen.
I understand your feelings about tinkerer and even share them somewhat, but running from fights never upset me, not even reloading the last save upset.
When it comes to enemies, tank target lowest health so healing those you want to protect can be more helpful sometimes. The healers should be healing because it keeps them from using the only attack they have. Drainers only bubble if you give them the option to and even that can be helpful because it resets their drain bonus. Tinkerers I have nothing yet, just hope it's nothing too bad to deal with, don't care for them much ether. Only tip with them I can give is if all 4 spots are full they should be the first enemy you beat.
Honestly a healer having an attack spell makes sense, a tank being able to deal damage makes sense (bleed is the real killer). Though I could see swapping bubble and the spell I feel that would be more annoying to deal with.