Usually a lot of absorption creates a MF and HF reflection free zone around the source and mic. While this will obvious not sound lively to the ear it usually doesn't actually sound dull. Do you find conversational tone dull outdoors?
The much dumber mono mic makes this blatantly obvious. Dead vocal booths deliver sparkling clear vocals due to the lack of reflections. Problems can occur if your LF treatment is inadequate at the bottom end of the vocal range. e.g. A square room resonating at 80Hz needs extensive LF treatment. However do note that such modes have locations. e.g. A cubic room resonating at 80Hz will have little or no 80Hz at half height, room centre.
The lack of reflections can be disconcerting. However, unlike acoustic guitar, fiddle, drums, the vocal chords are not significantly affected by room return.
Thus you can easily establish exactly whatever you need to perform using decent headphones and a good reverb.