Is there any way to deal with the high degree of centralisation that Bitcoin has?
First and foremost, to be clear, this is about centralization of Bitcoin as a native currency and not of Bitcoin as a network itself. Bitcoin as network remains decentralized whether the large bulk of BTC are in the hands of a few or well-distributed across the community.
As to what we can do to the current status, I don't think there's something we can do about it. But there is definitely a way for things not to get worse. I guess it helps that retail Bitcoin investors be properly educated of the potential of Bitcoin itself. If they remain as mere speculators, as pure Bitcoin investors who are only after the money they could gain from its price appreciation, they are more likely to sell upon profit. In which case, they are most likely selling to the whales who are acquiring and acquiring without selling. This is the reason why Bitcoin is focused on them. It is not only the fact that they can afford.
But if small-time owners of Bitcoin learn to HODL in good days and bad, this centralization wouldn't become worse. Furthermore, if Bitcoin consciousness becomes more widespread and new retail Bitcoin owners would begin to stack Sats little by little instead of selling, this situation wouldn't get better.
In the long run, however, a stronger demand will neutralize the impact of whales suddenly selling in bulk.