F2pool, Ocean pools are going to be outliers here, simply put, F2pool censorship transactions for political agenda, Ocean censors ordinals/BRC20 tokens, mempool has a similar and better looking indicator called health, here is an
exampleI thought MARA was the only one, disappointing to see others following in their footsteps as well.
Other pools that have acceleration services like Viabtc will also have some bad selections for obvious reasons (I talked about how Viabtc scam miners in the past), you also have propagation delay issues, so the perfect set of transactions isn't always the same on all nodes, your node may be seeing 10 good paying transactions that mine doesn't see at the time of solving a block but you would think that I missed on adding them because my LP solver is bad.
Yep, that is amongst other things like directly pushing TXes to mining pools (some of them are including non-standards). Another good consideration is the delay between the block being mined and the refreshing of the merkle root; merkle root isn't refreshed in realtime and I presume there are instances where new transactions are seen after the block is mined.
I don't know if any pool uses LP solver post/prior to getblocktemplate, i'd assume the safe option is to do it before and not after since getblocktemplate will do the verifications needed to ensure your block gets accepted by the network, your LP may add a transaction that would render your block invalid, I doubt that any pool is willing to risk a whole a block just to add a few sats to a 6-7BTC block, but as you mentioned earlier when fees make up a majority of the total rewards it would be worth the effort and the risk.
Possibly not actually. But given how many invalid transactions were being mined by pools previously, I wouldn't be surprised if they're evaluating and building block templates themselves.
What I wanted to highlight was actually the size, because it is consistently 99.94/99.95% for F2Pool and less for others. The way that they're selecting the transactions is probably better in terms of quantity, or they have another pushtx utility. The txes being pushed are quite sporadic and I don't see any within the day or two.