what I discovered so far is that any power up that involves 'charging' is shitty.
Very wrong.
Usually it's the opposite. Brimstone, Mom's Knife, and Monstro's Lung are all top tier items. Even Chocolate Milk, which used to be terrible (imo) is now very good as its synergy with Brimstone has been repaired (brimstone) and as you can ignore the charging and instead use rapid fire.
The only bad charging item is Cursed Eye, and that's mostly because of the terrible teleport effect.