I'll be completely honest, I've been kinda unsure about the direction the metagame is going. I believe it was
Acast that said not to long back, "Higher used types are being used more, and lesser used types are being used even less." I feel with the recent Aegislash ban, for Ghost at least this will be more so drastic, and it's beginning to become more evident. Granted, there's reasons as to why a lot of these types are used so less, its because they typically have very strong weaknesses (ones that are prominent in the current metagame) that cause them to typically lose a lot more than they will will, and as what
EienSeiryuu was saying, types like Psychic are near fullproof if used right.
I was actually talking to
scpinion 1 day just debating about the recent ban, and there's 1 thing in particular that really struck me from our discussion. There used to be a philosophy we had that stated that we'll try our best to make every type at least usable. I noticed it was removed, and during our talk he talked about the integrity of Ghost as if it didn't matter at all. What frustrated me most was that this was a type that was highly doable to ladder with, as numerous people had great success on the ladder (granted it was difficult I could imagine, but very doable). He did mention UU Monotype being a place where these lower used types can thrive, but, its not an Official Metagame, its just a Monotype community-driven one. Yea its fun, but when are you really gonna play this metagame competitively? There's not gonna be a ladder for it, and there will probably be much less tours for it than with the main Monotype Metagame.
The point I want to drive home is, why can't we try to make it so that these types can at least be doable in the current metagame? I'm 9.99 times sure out of 10, people do have bias towards their favorite types, and will often use that the most out of everything. Now I'm not saying we should repeat what we did ages ago unbanning Kyurem-W and Skymin, but why not put this into consideration when we're talking about potentially banning or unbanning a major element out of or into the meta? For example, the problem with Psychic going on right now mentioned above, Ghost could actually flourish to balance that out a bit, and it itself would have more usage. But with the Aegislash ban, its near impossible to ladder with it and do "good." Now you could compare Ghost with Ice in the fact that Scizor completely wrecks it. As mentioned in the OP, even with Scizor banned, Ice would still not do all that good, and Steel would still have a good chance to wreck it, while we nerf a non-broken type. It in the end all depends on with what we were to gain, and what we were to lose. Ghost was by no means broken, and Aegislash alone wasn't, as we know the reason it was originally was banned on Steel was because of the broken Immunity Core it formed. When Aegislash was banned from Ghost now, they lost a key defensive pivot, and one of few Physical/Mixed Attackers, and there isn't really anything that can full proof replace it, and the type's now plummeted in viability.
Tl;Dr I think next time before we make a major decision that could affect the metagame, we put
ALL 18 types into consideration. Each one should have the opportunity to be at least usable, and be able to have a chance in the competitive metagame.