its to say that if ur opponent is running airslash they have completely crippled one of their best pokemon for fun and it is now easily beatable by a slew of extremely common mons AND any form of passive damage. ever. thus, if your opponent has airslash yard, it is not scary at all since it lacks a core option and you at worst get cheesed by airslash on kommo and then claim their mega slot or, (because most yard cores make very good use of its sun w/ bolt and tusk at a minimum) you now freely prevent those other pokes from reaching their intended potential over the course of the game because yard is easily snipeable
So, you brought Kommo-o as a check to take advantage of Mega Charizard Y. Cool. It cheeses you with Air Slash, now what?
In the teambuilder, now we're going back to the other checks already, so why run Kommo-o to check it in the first place? Throw a Toxapex and put up Tspikes, SpDef Moltres is a consistent check, gamble with Mega Tyranitar instead of gambling with Kommo-o, because Mega Tyranitar turns off the Sun and lets you get Rocks or Pursuit trap the bastard.
No, most Pokemon do not just snipe it without Scorching Sands, because Scorching Sands completes its coverage of Weather/Solar from killing 90% of Pokemon to killing 90% of Pokemon + 2HKOing Raging Bolt, burn chance on Mega Tyranitar and killing Heatran. Those Pokemon are the main stopgap checks to it, so that is the much better move over Air Slash, but saying "Well they ran Air Slash now they're cooked" is just wrong unless you build your team with the idea that if Kommo-o gets sniped by Air Slash you have other checks.
So why not just run the other checks. That are better. On Average. If Kommo-o did more in general, I'd see the point, but these other Pokemon do a lot more stuff and also put up Rocks but also have other utility. Mega Tyranitar can click Knock Off, Toxapex has Toxic / Toxic Spikes / Knock Off / Haze /whatever the hell you want, SpDef Moltres can be a pivot or Defogger or just try to catch people with Flame Body, can also run Toxic if you'd like, etc.
And to be clear, I know the counter-argument here is "Well it has synergy with those other-" no it really doesn't. Mega Tyranitar nullifies Kommo-o's Lefties if you're running Bulletproof, which you should since with Overcoat Weather Ball is still 3HKOing your ass, I'd say that's fairly anti-synergy especially if you're using Roar (which realistically means you're taking a hit too) and Toxic stalling. Toxapex being a potential Hazer + having its own hazard (which is more unique and generally harder to run) makes Roar Kommo-o not really seem that appealing to me. Heatran, sure, but also why not Heatran + Mega Tyranitar, or Heatran + Toxapex, which are good. Similarly, SpDef Toxic Moltres already checks most of the Physical Pokemon and can include stuff like Volcarona, which people are pairing with Mega Tyranitar a decent bit (SpDef or PhysDef).
Roar and Toxic is okay utility, but it isn't to the level of Knock IMO and the fact that it's a bigger gamble makes me not see the point of running it, at least on ladder.
Kommo-o is probably a good Pokemon for this role probably in a tour match (wanna make this clear, I am arguing from the POV of ladder shitter) where you can be 90% certain they aren't going to be running Air Slash, but if that isn't the case then I don't see why you'd run this on ladder.