The play for colossus is to switch to slayer, sadly.
Demolish is a one trick pony attack and has many, many counters and if you don’t land your final hit, you are just terribly behind. Demolish grants you snare (while also slowing you down to a crawl) and stun immunity… but nothing else - any other kind of CC will stop your demolish. And it’s just not powerful enough.
Slayer sims higher, gives much better mobility, and speeds up bladestorm CD. Colossus is hot garbage.