Do retail investors really need to learn all about block builders, builders, and bundling? I think it's unnecessary. Just knowing that "someone might take your transaction and bundle or reorder it, potentially changing the execution price" is enough—don't scare yourself.

My assumption is you're not trying to front-run hot spots or do ultra-thin slippage arbitrage on-chain; what you need to do is more practical: avoid pushing the market price in low-liquidity pools, first reduce slippage, split orders when possible, and prioritize using protected routing/private transmission (at least don't send naked transactions into the public mempool).
Recently, rumors about stablecoin regulation, reserve audits, and de-pegging in the group keep changing—it's the same principle: emotions are most likely to make people "rush to trade," and frictions will take advantage of that.
For now, being able to calculate slippage and fees clearly already puts you ahead of most people.