So after playing a few hours on the stage with a few friends and some people on Anther's ladder:
the platform under the stage is useless, I don't see anyone going there except for recovering and then moving back to the stage. Otherwise it has no real use. Camping it seems pointless. You can't hit them above which is the major thing.
The walkoffs platforms can be annoying, but since you can hit from below them you can try to approach. Still risky however.
The stage does seem rather huge, which is good against zss and sheik.
The floating solid platform can be hit through with DK's upair I've painfully discovered. So although you can't jump through it, some characters at least have hitboxes large enough to poke through it.
My biggest gripe with the stage is actually visual, it can be rather bright at times, and when the monster roars it's distracting for sure. But the lay-out seems fine. In areas that allow Delfino etc this should be a no brainer to be legal. Delfino is way more brutal with getting so close to the blast zone.
It seems to have it's use against the top tier characters. It does needs to be played in quite a few weeklies/tourneys to see if it produces too many boring parts during a match where they camp things out (like the walkoffs, the platform below the stage. Some characters could abuse it in ways I haven't thought about )
edit: Some numbers: in training mode against an npc mario (whlst using Mario) (0 di, no rage, no staling)
Mario get's KO'ed from the ground with a fully charged upsmash at 81% on Battlefield
Mario get's KO'ed from the ground with a fully charged upsmash at 81% on Umbra in the first bit and then becomes 82% onward (might be error on my part or blast zone shifts slightly up)
Mario side smash kill at 80 % in the middle of Battlefield against CPU mario
Mario Side smash kills also at 80 % in middle of Umbra.