I see no problem investing in ETH to be honest, ETH is still in the lead, IMO. As long as you will use it, I don't know why you would be worried in the first place because it will not affect us as users.
Same here, ETH market is pretty solid and it has liquidity. We don't need to be seriously attached to a cryptocurrency so whether it is centralized or not, as long as it will give us profit, why not take the opportunity to earn from it. Meaning, if we find the ETH market profitable, why not take advantage of it. We are just buying it to sell in higher price anyway.
If you only care about the profits what you say makes sense, but things are never that simple, just take a look at what it is happening with coins which were centralized like Luna and FTT, and even if ethereum has way more trust supporting it and it is nowhere near as vulnerable as those two tokens, the fact that it has become centralized means that it can be more easily manipulated and as such a collapse like that is not out of the question during the next decades, and if you are invested in ethereum at the time your losses could be very high.