People would perceived that BCH or BSV community acknowledge BTC is superior in some ways. There's no way BSV community and faketoshi would do that.
but they can't inject themself into a transaction
It depends on sighashes. And if mempools will be permanently flooded, then batching will be needed, and there will be services, which will batch transactions, and grab some fees for doing that. But yes, users have to agree on that, by constructing a transaction in a different way. And if you have a choice: create your transaction alone, and have 1 GB of other pending transactions before it will be confirmed, or batch it, and get it confirmed faster, then it is not that hard to imagine, that many people will choose batching, if that option will be available.
Rather than services, we might as well as add protocol which allow non-interactive cut-through or CoinJoin.