A transaction is rather fast on the Ethereum blockchain. I've had reddit posts that took longer to settle than Ethereum transactions.

Ethereum is also not in a finished state. Scaling options haven't been fully explored yet. The move to PoS alone should decrease block times.

Historically, discussions were done in Usenet on much longer timespans, so this shouldn't prevent using it for real discussions.

Ethereum is a DAG so the block time is very low, like 10 or 15s.