I have run a heavier flywheel in a KTM 450. I didn't intentionally do it but I did a stator upgrade that came with a larger and heavier flywheel. I my case I run a Rekluse so cannot comment on the potential for it to reduce flame outs but I would assume it would be an improvement in this aspect. As far as smoothing out the bottom end "peakyness" I would say possibly slightly different but not significant.
Are you trying to deal with a specific issue or problem?
Flame out is an engine stall in low speed manouvers. Occurs much more frequently in the dirt but have had a couple in the snow. My 2015 Husky FC450 is bad for flame outs. Non-issue once you go with a Rekluse.
Some of the race model bikes have light flywheels. This allows the motor to rev quicker. That's great but the trade off is that you don't has as much inertia turning the motor between compression strokes. So sometime when you left off quickly you can have a flame out. With wheels the bike rolls easily but with a track there is a lot less roll.
If you have a ktm xcw or exc you already have a much heavier flywheel.
Test have been done adding weight to flywheels and I believe you can add around 10 oz. Of weight to a race model flywheel without it robbing any horse power and reduce flame outs but it will slow down the rate at which the motor will rev up.