Any use for Ho-Oh?

I can see it a superior counter to Lugia for a steel machamp, using the ES/Brave Bird combination. Not sure how effective brave bird is given its tragic damage per use, but the 1.4x super effective should help.

For now not really. But who knows if he gets other moves in the future, they change stats, pvp or they make defenders relevant again including the legendaries.

And if not he is at least +1 for the dex

Bulky Generalist? But don't think its defensive capabilities are superior to Lugia.

Pokedex filler.

Even Flareon and Arcanine are better.

"It has sky-high defence, decent attack.
Solar Beam without STAB."

All true. I like to think of Solar Beam as being Hyper Beam with STAB built in. It's got enough power (180) to not need to worry about STAB. Take Typhlosion - he can have Fire Blast (140 + 28 STAB = 168) or he can have Solar Beam (180). Doesn't need the stab to be stronger. There's a reason nothing in the game with a super high CP has Solar Beam, until now.

That said, Solar Beam is slow, easy to dodge, and takes a long time. But it brings the damage like no other move in the game.