The huge mistake would only be if you up your travel and can spend more on the PP card. Obviously once the card has been dropped by you, you cannot get it back although I am told that the FPQPs only end with the expiration date, if applicable, even if you drop the card.
This card has been quite useful to me and I think it is likely to continue to be because the CC earnable PQPs are good to 10,000 PQPs and are good for 1K and the Plus Points beyond.
If you really don't see a lot of travel in your future the explorer card might be enough, I would miss the UC even if the experience has become inconsistent.
As for elite strategy the target has to be to aim for Gold if 1K is not feasible so I personally would not aim to hang on to Platinum and would look to get Gold if I expected to do some travel, especially international with Gold's *A Gold benefits. If by applying all to get to Silver in 2024 gets you to Gold or Platinum in 2023 that might work for you.
I am hoping that UA may leave the qualification levels where they are next year and not provide promotional PQPs.