So I feel like there's a theme to your post, and the theme is "no single counter against a scathis is guaranteed to work and easy to pull off", which I think is absolutely as it should be. If team scathis scouts your counter, they should be able to defend against it. Its not unbalanced or OP just because its possible to prevent counter attacks against it if they're scouted.
I also note the lack of a response to double nukes, which I can only assume means that not only think that will work, but you think it will work well enough that it wasn't worth responding to it.
1 T3 artillery will almost never do anything. 1 T3 artillery is stopped by a couple of shields. Since you're building the scathis under protection of shields anyway, it's very much possible to build one and keep building after your opponent finished the artillery.
True, but you get a second up after only 30k more mass, with a faster build time, and with less mass and resources spent on defending it because it isn't on the front line. Because its farther back, nearly every counter you'd use against a scathis is more difficult to pull off for the arty. And yeah, it may not directly counter the scathis, but it does give you the ability to target eco, and if you've rushed the arty, it may come up before all of your opponents power is shielded, or it can be used in conjunction with other attacks like gunships, bombers or nukes. At minimum it forces the enemy to spend a great deal of their eco building shields over everything.
The point is that even if the scathis got a damage increase, T3 arty will still be a viable option with its own advantages. The scathis might drop your firebase and outer mexes quickly after being built, but your arty will have been firing longer and you can expect to have more than one of them shortly after the scathis has been built.
An ACU tele snipe will cost an ACU, so it will cost a player. SCU's telesnipe is more difficult to deal with, but you need multiple SCUs which costs an insane preparation time. If your opponent is getting them, there's other stuff he's not getting. With teleport, it's always a matter of paying attention. Paying attention is OP against teleport. Just move the scathis when you see it, move it back after the SCUs have died.
Trading a player for a 110k mass unit doesn't really seem like its that bad an idea, the enemy is now in the hole. It may not be your first choice, but it certainly works and should not be discounted as a counter. Yes SCUs take a great deal of preparation and are expensive, but so is a scathis. I find the strategy of moving the scathis to not be serious though, it has a deploy time and is slow as hell. To move it you'd have to 1. Have already spent the 110k mass cost to build it (its not still building). 2 Have scouted the tele SCUs with time in advance to undeploy and move the scathis. I feel like what you're really saying here is that tele SCUs are not guaranteed to work, but neither is building and deploying a scathis.
They are effective at this. It's what bombers do. It's also the only thing bombers can do when attacking an enemy position. After that, they're dead. With properly layered shields, and using air properly, 20 T3 bombers are also not enough.
Yes, bombers can be countered with shields and AA. When 20 bombers is not enough, you can use 30 or 40, its still much cheaper than a scathis. If your enemy has managed to both build a scathis and kept air dominance then I think you deserve to lose.
Air drops are horrible when there's a stalemate that allows for a scathis to be built. Not a single air transport will get through.
Air drops are horrible when you're trying to drop past the front line in late game team games. When you're trying to drop on the front line I don't think they're as bad as you think they are at least if you plan it effectively and work on removing their T3 air before making the drop. Morover, they can be used as a very quick counter. You likely already have some T3 land units so you probably just need the transports to do this. Aside from getting air dominance, there's not much involved in terms of prep.
And three Aeon TMD protect against this Also a good deal of other TMD will work, in combination with shields. Doesn't mean that it doesn't work, it just stops working when your opponent pays a single second of attention.
Yeah, Aeon TMD is pretty ridiculous, but TML is just one of many options at your disposal. I didn't mention T4 assault bots because they're countered by nukes, but there's a theme here. Yes, everything has a counter, no that doesn't mean that powerful units are OP. If your opponent has nukes to counter a land push + enough SMD to stop a nuke or multiple nukes + enough air domainance and shields on the scathis that he has near perfect scouting to move his scathis out of the way to stop tele SCUs and can also stop bombers or mass T3 drops on the scathis + enough shields to stop significant damage from a single T3 artillery now and another one when you get 30k more mass then you are just dead. And you should be dead, and you didn't die because of the scathis, you were just outplayed.
And after the loss, maybe you'll blame the scathis, and ignore the stunning mass disparity that team scathis must have had to do all that. Maybe you'll blame it and claim that a scathis worth building is automatically OP on 10x10 maps, and maybe the balance team will listen to you... but none of that means that it was really OP. It just felt OP because team scathis was so far ahead that they were able to build the thing on the front and were so dominant that they were able to scout and stop all counter attacks while pouring 110k mass into a fragile unit that they had to build and defend on their front line.
Anyway, its worth saying that if everyone really believes that a scathis cannot be balanced on 10x10 maps and must be in its current state which is never worth building in any circumstances then you can change its role to something you feel is balance-able or you can remove it. Just don't leave it in the game if you can't make it useful for any particular purpose.