That's complete BS; if you can't figure out how to recover from underneath Battlefield then you need to do some more experimenting. It's definitely possible to recover on Battlefield if you accidentally fall underneath, but it's sort of impossible on Rainbow Cruise if the platform just stops existing.
I'm sorry but do you suck?
Battlefield's ledge is ruthless. Many characters on many occasions simply refuse to grab the ledge, for god knows why.
As for recovering from underneath Battlefield, I don't see how anyone but Samus or Jigglypuff can do it. The overhang ruins people / a lot of characters. And you can use that to your advantage if you learn to abuse it.
Provided that it's not Peach who is just floating underneath it to be difficult.
You also need to be dumb or blind to realize too late that the flashing platform is about to disappear. I agree that you can die easier on it than say FD, but..so? Just play smarter and learn to play on it. Because you're both at the "disadvantage" of those "tricky" "platforms" and it being "impossible" to "recover" "from"
As for your direction to where Rainbow Cruise is on MLG rulesets, Pro Kirby User, I'm at a loss. Looks bad on me, but eh whatever. I remember seeing many MLG random matches though on Rainbow Cruise, maybe it's been taken out since then.