Steel in general I'm ehh on. Sure it only has 3 weaknesses, but:
- Those 3 weaknesses are among the most potent attacking types.
- Nearly every attacker worth its salt carries a move just to hit Steels (plus as mentioned those moves are of great offensive types in general), so mons we check on paper are often going to nail us. It's not as bad as it was in the days of Hidden Power, but moves like Mystical Fire and Close Combat getting tons of distribution this gen don't help.
- Steel is a terrible offensive typing. No getting around it.
Basically Steel suffers from being "too good" defensively, and has issues fulfilling the "offensive" part of "offensive team support".
As for Steel Electric, well what's the difference between that and pure Steel tbh. Marginally better offensively and now resists Electric. That's about it.
And I'd like to point out on the subject of Dark: There are two mons on the entire CAP VR that are Dark and use support sets.
Mandibuzz is a great mon, but realistically its offenses are so dire and its movepool so empty that it can't help but run support sets. It has no offenses at all, and really its support pool consists of Knock, Toxic, Taunt, Defog and U-turn. So it's really just a hazard removal pivot that Knocks.
Grimmsnarl literally is made for support with access to Prankster. It makes a great dual Screens setter and can also run a Bulk Up set. But it can't do both. It has to choose between being a passive but effective HO support or a solo threat. And it doesn't even get Knock.
Worth pointing out that both of these have a secondary typing that neutralizes their U-turn and Fighting weaknesses, which would otherwise make their job a lot harder. Looking at both of these, I'm not seeing where Dark's supposed large support pool is coming from. Because there are 0 Dark mons on the VR that even come close to having a deep support pool that they regularly use. So again, STAB on Knock Off woo. I really don't want to get to the point where we have to make another Mandibuzz with terrible offenses or gimped movepool just so it doesn't turn into a Knock Off Attacker. Because Colossoil, Bisharp, Crawdaunt and Obstagoon can tell us all about that (despite several of them being blessed with a support pool to ignore). And it we do gimp its offenses so it doesn't turn out like them, well we just made a Drapion, Incineroar or Pangoro for the lower tiers. Heck, Malaconda gets Knock and a good support pool, yet no-one uses that. So no Dark please. Game Freak has thoroughly explored this area, and the conclusion is that STAB Knock just means a balancing act between making its offenses decent so it doesn't flop and not giving it the tools to just become a breaker.