The way users of v2 effect the safety of v3 and the tor project is in terms of directory and resources, etc, and potential exhaustion attacks native to v2. But

The way users of v2 effect the safety of v3 and the tor project is in terms of directory and resources, etc, and potential exhaustion attacks native to v2. But with porting and some work most of this could be mitigated. The safety of the hash and the length used couldn't but there still isn't a real world example of a collision in use. It's pretty drastic to entirely throw away 15 years of inter-linking, indices, etc when <5% of users (probably less) of onion services have switched to v3.