Ideally we would be better with increased decentralization. It could be a problem if they colluded and attempted to censor or double spend. Chances are they won't, because it will probably negatively affect their own bottom lines (reduced confidence in Bitcoin leading to reduced value of their own assets).
Secondly, any blatant attack on the network could be countered by the participants forking in a change in the algorithm used to do the proof-of-work. This would bankrupt the attacker because they would be sat on enormous amounts of now useless mining hardware.
https://www.blockchain.com/en/pools