Honestly, I can't undestand the reason why Full RBF has been pushed so much.
0-conf are a bitcoin use case, even though not advisable for large amounts.
The main thing that got the mempoolfullrbf option added to Bitcoin Core was the fact that full-RBF mitigates a variety of double spend attacks on multiparty protocols like coinjoin.
Basically, double spends are ok in multiparty protocols. But what isn't ok is people double spending in a way that causes transactions to take a really long time to mine. Full-RBF is a major step to preventing that, because it forces the attacker to use a transaction pinning attack, which is expensive.
Unfortunately full-RBF is probably not going to help you with those closes, as it's more likely that they don't meet the minimum relay fee (I assume they're force closes).
The ViaBTC and Binance transaction accelerators could help out. As will the mempool.space one, which is a lot cheaper. But not publicly available yet.
I recently enabled this to on my Start9. I also enabled v2 P2P encrypted transport too. It says that it will drop to standard v1 as a fail-safe so can't see any reason not to enable it too, right?
I'm would not know the answer to that question. If you go on telegram Start9 community chat. StartOS support, Your question may get answered there. https://t.me/start9_labs .
mempoolfullrbfoption added to Bitcoin Core was the fact that full-RBF mitigates a variety of double spend attacks on multiparty protocols like coinjoin.