Talonflame and Mold Breaker Hawlucha aren't exactly top meta picks. Corv has plenty of use outside of just Defogging and sometimes doesn't even run Defog at all, whereas Talonflame and Hawlucha are extremely niche outside of their Defogging, having nothing even close to the longevity of Corv. I do think Talonflame specifically is pretty underrated because it hard counters most variants of Great Tusk and Iron Treads (although it hates getting Knocked) and can spread fast burn around, and Hawlucha has a nice STAB combo. But to address your central point, these just aren't mons that want to switch into Gholdengo or most other offensive mons more than once, so their utility as dedicated Defoggers is very limited.
Glimmora has no business being your primary form of hazard removal, Mortal Spin is just too easy to block and it does not have the bulk or defensive typing of Great Tusk or Iron Treads. It also gets stuffed by Gholdengo anyway, so what's even the point? Overall, I think you're heavily exaggerating both how strong hazards are in this meta and how much Gholdengo enables that. I definitely think hazards would be far less centralising than they currently are if Gholdengo was gone, its high usage is testament as to how valuable it is on hazard stack teams
1. Talonflame is actually good, though. It can run Defog sets or offensive sets. The Defog set tends to run Flame Body and Roost, so its utility isn't bad. Running offensive Talonflame means you don't get the advantadge of it as the Defogger and you need and to be much more careful about hazard clear support, but this is also doable. I've even used teams with offensive Talonflame with no boots and Corv as the primary Defogger, and it works against Gholdengo because you can just slap U-Turn on Corv and then switch into something that threatens Gholdengo. The threat of the opponent losing momentum and taking a nuke from something like Chi-Yu or Dragapult just because they wanted to block Defog can be an excellent deterrent.
2. You aren't using these mons to switch into Gholdengo. I don't know why, but a lot of people seem to forget that
Gholdengo has to switch into you in order to actually block hazard clear. This is both fairly predictable and can allow you to dictate play by punishing Gholdengo if it wants to switch in or using the threat of super effective moves as a deterrent for doing so. If you play right, Gholdengo switching into your team shouldn't be free most of the time.
3. If you need something to switch into Gholdengo, use a special wall that isn't weak to its STABs. It's not common that the hazard clear pokemon and the special wall will be the same pokemon. Toedscruel can do this, but it's a bit of a niche mon at least in OU and doesn't fit on every team.
4. Glimmora is really good. I've tested it as a primary hazard clear pokemon and Mortal Spin is actually pretty good at it. As I said before, it can run Earth Power and it has 130 special attack. So it doesn't lose to Gholdengo or most Steel types and most teams aren't designed to specifically spinblock Glimmora anyway. And if you are worried about Air Balloon, this is something that goes away with chip. Again, it's pretty easy to punish Gholdengo for having to switch into you.
I'm not entirely certain that Gholdengo is the most pressing matter to deal with in the meta to start, but I've really gotta voice concerns against the points which claim that Gholdengo is only on the radar because it invalidates Corv's Defog and that invalidating Corv's Defog is not that big a deal. I really don't think those two assertions are true at all and it's a disingenuous representation of Ghold's affect on the meta as a whole right now.
Gholdengo is undeniably a strong pokemon. It has a great typing, ability, and move pool. Does that make it OP? I don't think so. Aegislash in gen 8 was likely better. The OPness of the hazard clear block aspect of it is greatly over sold. Again, it has to switch into you to do that and this can be punished.
While you might think the Corvinikight point detracts from its overall impact on the meta, isn't that the biggest difference between it and gen 8 Aegislash? I honestly believe Corv would be overcentralizing if Gholdengo was banned.
so Mortal Spin Glimmora goes from “punchline” to “actual option”).
It's an actual option now. Just run Earth Power to hit most Steels.