The whole "but weak to knock tho" argument was used last gen, and respectfully, it's as weak now as it was then. They aren't "unable to do their jobs if knocked", Zap and Torn were still defoggers even pre HDB so that sort makes this silly. Your comment on defog Gliscor isn't really reflective of how it is. It wants to do other things? It doesn't want to do anything except what it's put on a team for. That's literally it's appeal, it's hugely flexible.
Gliscor fell to UU in early SM for several reasons, such as poor meta trends, but also because it was overlooked and underappreciated, and once it was realized it shot back up. It's easily able to outlast and beat just about every hazard setter, which is a big appeal. As for Lando, you DO know modern non Defog lando is an A+ mon right now right? Defog Lando is so good because it doesn't ease up on offense while having amazing defensive utility and were it around now, it would be on par, if not better than Tusk, for being Spikes immune is incredibly valuable.
You didn't really make a case for Tusk being the best, just commented on flaws the others had, and somehow that makes Tusk the best as though it were a flawless removal tool when it's not. Tusk is shredded by spikes/tspikes, is punished by static/flame body, can be spinblocked.
it's... really not. Like it's strong, but it has some pretty glaring issues that limit it (very hazard prone, slow, vulnerable to one of the most common types populating the tier, fairly limited in sets because of a rather shallow movepool). I really don't understand where this "Bolt is broken" idea coms from.
When your main job is to remove hazards, being weak to knock is crippling when you are weak to the most common form of hazards, stealth rocks. And in previous metagames, while spikes were amazing, they also were not as common as they are now. Thus, stealth rocks was the main hazard and again, being weak to them isn't the best. Torn at least had regen to heal off rocks damage but zapdos has to roost off the damage, and while zap is a great mon, it being forced to roost isn't the best. That lets something in for free and you haven't done your job as a defogger. There was HDB in Gen 8, but overall I think the most common hazard was/is still stealth rocks, so I consider being weak to them not the best.
Defog gliscor I will admit, I know less about. However, being relegated to UU at a time, is something that has to be taken accounted of. Defog was given to a lot of things in USUM, but that means normal gliscor wasn't able to cut it. You did say that it was underappreciated, which I will take your word for, but comparing it to tusk, I'd say it keeping off hazards is a lot more difficult. It doesn't matter if you can get off hazards if you invite the hazard setters back in. That's exactly why in Gen 6 only the Lati twins were good defoggers, because they could at least stop the opponent from just setting them back up again, and even then, they had issues such as being weak to pursuit tyranitar. Zapdos could attempt this with pressure, but that is more niche.
Defog Lando is the only one I can even consider being close to tusk, and I think it is edged out by tusk a bit. Sure, non-Defog lando is an A+ mon, but idk why that is relevant. Defog would mean it can get off hazards, and it might rise a rank, but this is comparing it when it had defog vs rapid spin tusk. It does have a spikes immunity, but tusk in return has better offenses (fighting+ground is insane) and can keep up your own hazards.
Tusk is definetely destroyed by spikes, but unlike zapdos, it can actually resist stealth rocks 4x, which means it can destroy many stealth rocks. It may be punished by static/flame body, but few mons have it. The mons that have static that are relevant are zapdos, while the mons that are relevant with flame body are Heatran (which commonly runs the much better flash fire, don't even at me), moltres and volcarona. Zapdos and moltres are definetely the biggest threats, but one knock off cripples them or a teammate, which I don't think is the best. Heatran is destroyed by both stab moves, while volcarona really doesn't like taking a headlong rush. I'd say it does fine into static/flame body mons. As for spin blocking it, the only relevant ghost mons that could spin block it are dragapult, gholdengo, aegislash and maybe mega sableye. All of these besides mega sableye are destroyed by knock off, with aegislash and gholdengo also destroyed by headlong rush. So I would say, no, it is not easily spin blocked.
TLDR, only Defog Lando-t is close to tusk, and I would say keeping your own hazards is enough of a benefit to give tusk the edge.
