Can you have a good fretless mwah sound without delayed bloom?
i think so, although once you hear that sound it's hard to let it go, right?!
IME/IMO: a lot of that has to be setup + technique. i arrived at setups that give me some choice (amount of mwah, the nature of the bloom) depending on where and how i make/stop/pluck the note. i'd say it's an "average" setup for me --- not too low (but way low!

), straight neck (but maybe not perfectly straight), and some individual technique on any particular ax (all very similar setups, but different feels from ax to ax). i get more mwah and bloom stuff by playing with a softer touch, usually closer to, or over the fingerboard. but i'll wanna be able to dig in, too, so it's a compromise in the setup, e.g., "average."
TBH, i don't play fretless to make "mwah" sounds. it's fun sometimes (e.g., ballads, some solos), but the music i play doesn't require mwah or bloom, per se. i like to have that sound available, but i don't rely on it. i play fretless because it's the easiest bass instrument to play (for me) compared to DB, fretted EBs, tuba, and maybe even a synth. YMMV.