Recently, people keep asking whether retail investors need to learn about block builders, bundles, and so on.

To put it simply, there's no need to memorize concepts; just knowing "your transaction may not be included in the block in the order you want" is enough.
Especially when you're making large trades on DEXs with loose slippage settings, or just catching the hype of new L1/L2 incentives to boost TVL, the chain is very easy to be packed or front-run, and the final experience often turns into the old users' complaints of "mining, selling"...
I'm not surprised either.
My approach has always been quite straightforward: split large amounts into smaller orders, tighten slippage, set limit prices when possible—don't rush to eat it all at once.
As for a deeper builder ecosystem, who signed what with whom, I no longer believe that "retail investors can win by learning these."
Knowing the risk boundaries and paying less tuition is enough.