Hmm, it could possibly come out but its requirement to activate the skill needs to change since duelists will have a hard time defeating Obelisk, Ra, or Slifer as soon as the fifth turn passes. (Just saying)
Not really, Slifer would be a trouble if you don't have a way to summon over 2000 atk monsters. Ra is truly bad with this ability, 0 atk and nothing special to do. Obelisk would be the only trouble, 4000 atk, can't be selected, but a Blue-Eyes deck with the field spell or beatdown with Gigantcastle/Cosmo Brain, Ultimate Ancient Gear Golem, Vision Hero Trinity, Elemental Hero Core, Onslaught, etc
Osiris is trouble even if you can summon a 2100+ ATK monster.
A 2100 ATK monster in front of Osiris is the same thing as a 100 ATK monster. Not exactly the most ideal thing to be in face-up Attack position. You really need the right Spell/Trap to deal with Osiris and Obelisk.
As for Ra, yeah it's trash. Especially if Yami Yugi doesn't have more than 1000 LP by the time Ra shows up.