Antoine,
Rejecting nodes with any valid tx in path, without this rule, is problematic, because it _can_ be possible for an attacking miner to engineer that scenario by grinding one TXID leaf to mask a subtree, which could have major consequences. Third party malleability vulnerability to deposit / withdrawal masking is a serious bug. Worth thinking that through very carefully before recommending these mitigations. Do you have an end-to-end working example of such a mitigation that doesn't have these issues?
> This is incorrect for any bridge, wallet, or deposit system that does not receive funds to a script that either burns the funds or that anyone can spend.
The problem is that from the perspective of a wide variety of layer 2 protocols, you actually do want to be able to simply close out a UTXO and prove a UTXO is spent.In the current L2 protocol design space, value doesn't always flow directly along the output, the UTXO may be being used as a connector input, and the spend of that output may be making a different output available after a timeout and excluding an alternative spend.