I2P is much faster than Tor. Largely because it isn't being targeted by DDoS. It's infrastructure is also better equipped to deal with user demand.

The network latency doesn't impact performance that much on bitcoin-core. It's more an issue for LN where payment time is a function of routing node latency. In core, the P2P network is how nodes relay pending transactions and propogate blocks. Latency is really only a priority if you're a mining node. Since blocks confirm on the order of minutes, a few seconds of latency isn't that bad.

However, I've experienced Tor requests that take many minutes or timeout entirely. So having a fallback anonymity network could be an infinite improvement in that case.