Which is why Choice Scarf isn't obsolete. It's makes revenge killers.
Why run Choice Scarf and potentially give your opponent free turns if you can just run Excadrill ?
The reason to run double dancing Terrakion is to handle threats according to the situation. If there's a Physical Wall, SD and knock it out. If there's a scarfer, use Rock Polish to outspeed it, simple as that. Your post made it seem as if Terrakion is facing those threats at the same time, which is impossible in the standard one on one matches.
If it SD's to knock out the physical wall it won't have enough speed to outspeed the Scarfer.If it RP's to outspeed the Scarfer it won't have enough juice to knock out the physical wall.
I can't be the only one that runs BOTH on the same team ?
What makes Terrakion special is the fact that it gets both boosting moves, its pretty bulky, and has STABs that provide great coverage in only two moves, and has really good attack and speed. Not all sweepers have that.
Terrakion does get both.However most if not all the time he will only have one turn and he has to pick which one boost he'd like.If your opponent let's you get both then that's his fault.
I can't see what makes this generations sweepers more dangerous than last gens.They certainly are not so dangerous that people won't run Scarfers anymore in fear of being swept after one turn of set up. There are more of them but you just handle them like you always did.