RBF is not a issue, is the natural policy for the mempool and as bitcoin always was intend to work. But full-RBF decreases the barrier for double spending 0-conf tx. This protocol allows for the two parties in a transction interact creating a nuclear transaction that uses 2x the price of the good being purchased as fees. This transaction is supposed not to be used, only if someone tries to double spend the first transaction. So this nuclear transaction is a threat of mutual assured destruction which avoids the two parties cheating at each other.

Good point. It could be a problem, although protocol allows for signing different transactions with increasing higher fees. Also is important to compare with lightning wich is the alternative for instant transactions. The penalty transaction will suffer the same problem of congested mempool. Wich protocol is better comes to personal risk choices.