This goes out to not just you, but everyone debating here and anywhere else on this forum, please read the characteristics of a desirable metagame, it outlines what we as a community want the meta to be like and offers explanation for many proposed bans. Rank destroys stall, creating less variety in the meta, an undesirable situation
The problem is rankurusu is not the only pokemon that makes full stall so hard to use without using "bad" (and I use this in the loosest way possible) pokemon or "niche" strategies. It's just the current one being scrutinized. So the question is do you ban a ton of pokemon so full stall can work again or do you just let it die and keep pokemon in the metagame. Which one really offers more variety?
The path you want to go down would result in banning more and more pokemon because as new gens come out, there are new and more powerful threats that have to be dealt with by 6 pokemon. It's undeniable that full stall will eventually die and by banning every single threat that comes along and causes it problems, you're only delaying the inevitable and not really doing anything favorable for the metagame.
In any case, stall can still exist but you need at least
some pokemon that can hit hard. Full stall just isn't that good anymore but it's not horrible either. You just have to expect that if you come up against one of the pokemon your particular choice of 6 pokemon can't deal with, you're going to get swept. For some teams, that's ranku, for others it could be terrakion or jarooda. I couldn't find room to fit in a mach puncher so I have problems with cloyster of all things.
On another note, I saw a sub/disable gengar that deals with CM rankurusu pretty well. It switches in on a CM/focus blast or after something dies. Then subs and disables the only move that hits it which is psychic or shadow ball and proceeds to kill with shadow ball.