If the hashrate comes down so extremely the 'mining part of the world' would try to get any mining machine as the profitability would go up even for non-profitable miners.
Not until the difficulty adjusts, and if that isn't going to happen for a year then it makes no difference. If the difficulty is based on a hashrate of 200 EH/s, and you have 100 TH/s, then it will take you the exact same amount of time (on average) to find a block whether the other 199.9999 EH/s actually exists or not.
but wouldn't there be a way to improve BTC's algorithm to consider a large and fast variation of its hashrate (maybe with an average time of the last 50 blocks or any suitable system)
Some altcoins have attempted this, and it has often resulted in miners gaming the system to maximize their profits, generating lots of blocks in quick succession and then very few for a sustained period. Having a fixed difficulty adjustment also protect against some kinds of Sybil attack in which an attacker could trick you in to accepting a malicious chain.