Witch and Thief are Meta by a ridiculous margin due to the Spellblade being not great compared to the Witch and the Thief being the only source of sneak damage. Witch is best built with tons of capacity and speed, and a little power to get her above certain break points out of the gate. You can also give her some metabolism, but quicker digestion leads her to gain weight quicker which in turn means she gets the speed penalties quicker.
With enough capacity, and a support unit like Priestess or Bard siphoning her stomach contents, you can actually get away with her not getting a significantly slower a cooldown until you are already done with the level.
Metabolism is better put on a support unit that will be pocketing the Witch, refreshing her cooldowns and keeping her from getting KO’d. The Warrior, Knight, and Bard make the best candidates for this due to their base speed.
I think a heavily leveled Illusionist may possibly replace both the Witch and Thief in team slots once she goes live, as her slow base speed can be remedied with a pocket and covering two important elements with a full screen attack will be too good to pass up.
I can see the next patch meta being Warrior, Bard, Priestess, Illusionist. 3 characters capable of supporting and lowering cooldowns, and all elements covered.
I could see the Bard being subbed out for the Thief or Witch in certain levels with heavier focus on physical damage or magic, but you rarely need to double up on elements, so meh.
Generally speaking capacity is important on every character, but especially so on damage dealers.
Metabolism is better on support units, although a level or two won’t hurt, especially early on when you can’t stack capacity.
Every character should probably have a few points of power, but it largely comes down to preference. I personally like 10 base attack minimum for every character. I generally pump attack on the Warrior as her excellent base speed lets her siphon off weight from other characters rapidly, much more so than the other support characters. Add in some metabolism to keep her stomach low, and you have one of the best pockets in the game. The extra power will also boost the amount she can siphon off at once and boost her defense buff.
Speed is the most powerful stat, but it takes a lot of investment to really reap the rewards. It should be the last thing you build due to how much it takes to get out of it. Use support characters to tide you over until you can invest in it.