Prestiging against Blissey

Depends on Blissey's CP and moveset. Try a level 30 Machamp vs level 30 Blissey with Zen/Gleam and let me know how that goes. You can win, but not with half time left, or much health. Machamp is good, though, I'll give you that much.

Trying to go down to half the Blissey's CP is too hard.

I was prestiging a level 8 gym with an annoying ~2200 CP Blissey at the bottom. I settled on using two ~1600 Exeggutors with Extrasensory/Solar Beam to struggle past the Blissey, then train more easily against the the next three pokemon at ~2600, ~2800, and ~2800. Not the most time efficient training, but I have been in that gym for over a week now, so I think it was worth it.

Blissey and all defenders were nerfed after they made quick moves fast again...

Timeout is much less of an issue for a lot of mons due to increased power of charge moves and quick moves being quick again...(faster energy gain)...

If this was the old system, then Machamp can still win, but timeout was a much much bigger possibility.