Why would you use Lati@s over Giratina-O? Seems like the only real advantages are Roost and Speed, which doesn't make up for Giratina-O's overall superior bulk and more useful Ghost-typing.
As for Solgaleo, I think reliable recovery, Speed, and superior coverage options make it worth using over Aegislash in a tank role. "Worse support moves" is a flawed claim: the only substantial support Aegislash has over Solgaleo is Pursuit, which it cannot fit over Shadow Ball if it wants to properly exercise the defensive niche it does boast over Solgaleo (beating Mega Lucario). Solgaleo is also less prone to giving stuff like Ho-Oh free turns due to wide auxiliary coverage and good Speed (given that Ho-Oh isn't overly bothered by Toxic thanks to Regenerator).
I also severely doubt that Solgaleo is blatantly worse than Klefki or Jirachi. Klefki is an awful role compressor these days due to the Prankster nerf against Dark-types and inability to beat Rest Xerneas - while Spikes are a big advantage and still make Klefki worth using, Klefki needs backup against most of the things is it supposed to beat which makes it not nearly as splashable as it used be, really only finding its way on Ho-Oh + Arceus-Dark balance teams. Jirachi's lack of Levitate and 4MSS between Wish + Protect + SR + U-turn + Iron Head + TWave or BSlam make it worse than Bronzong in my eyes.
Ferrothorn and Bronzong are legitimate competitors (as are Celesteela and Magerna to a somewhat lesser extent) due to wider defensive utility, but they lack Solgaleo's reliable healing and/or ability to ward off Fire-types with its combination of good Speed and coverage.
I also think Solgaleo's offensive ability is perhaps better than people give it credit for. Sure, it has kinda lame STAB types, but it gets a lot of coverage, some boosting options in Z-Splash and Work Up, and some interesting lure potential between Z-Crystals and type resist berries. The metagame is still quite young and there remains a lot of room for experimentation. Gen 7 is not even 2 weeks old, don't be afraid to just try stuff lol.