First off, be aware that BIP125 doesn’t prescribe any community (“consensus”) rule. A Bitcoin node might not comply with this alternative coverage. In reality most nodes on the community are operating Bitcoin Core, which implements relay guidelines near however completely different from what’s described in BIP125 with regards to alternative, and permits a few of these to be configured (for example see -mempoolfullrbf relating to BIP125 signalling). A part of the coverage carried out by Bitcoin Core by default is described right here.
If most nodes did not implement obligatory BIP125 signalling, RBF could be superior in all points to CPFP from the angle of the emitter of transaction. CPFP is a lot much less environment friendly, and never at all times attainable: you want the transaction to have a change output and (at the very least on the time of writing [0]) the guardian to move coverage checks by itself, for example if it is under the minimal feerate of most mempools on the community you will not have the ability to CPFP it in the meanwhile.
From the angle of the recipient of a cost, CPFP is the one different that does not require coordination with the sender.
Your second level appears to imagine RBF requires a change within the protocol. It does not, it really works in the present day. If something it’ll be made simpler to make use of sooner or later (by varied protocol enhancements, and the push for having nodes permit to additionally substitute transactions that did not explicitly sign for BIP125 beforehand).
[0]: bundle relay would repair this.
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