But you still get that xp, and maybe more, if you fail. For instance in a recent run, my xp for the first level was a decent 75. I couldve taken the bonus which would netted me a total of about 112. Instead, i kept going, made it about through (and defeated) the second boss and now can claim 281 (181 +100 bonus - later edit: and finished just past the third castle with 245 total xp). So basically, you can eclipse any bonus if you can make it through about half the next level. If you’re really beat up in the boss fight - just take the bonus and try again. If not, go and see how far you can go. Or maybe you’re just tired of this build or class, then just cash in and go again. I dunno, I just don’t see it as a penalty…
Oh, and I’m trying a run as queen now, to refresh my memory on her mechanics - I find she’s the opposite of what you’re saying. At lower levels, she’s really powerful - able to wreck lower mobs and bosses because their simple patterns are easy to interupt. At higher levels I find she struggles - the damage from the curse is greatly diminished at that point, and reliably interupting higher level mobs from using their abilities is increasingly difficult. But it can be a matter of picking your fights too - avoid mobs with locked abilities or requiring high card counts to trigger (since you’ll be trading 2 cards for one of theirs, often the value of your two cards exceed what you’re getting), and focus on mobs with exacting criteria (4 card flush, 3card straight, one of each suit). Also be really careful of mobs relying on black cards - since your key ability gives you all the spades, this is what you’ll fall back on to fill out your hand with cards, and probably be left to trade with when all else fails. Oh, and hex - avoid mobs with hex since it’ll interfere with your ability to swap cards effectively.