Getting rid of voting would do nothing to combat spam. There would be plenty of other ways communities could (and would) get spammed, not to mention how impossible interacting with and navigating communities with thousands of users would be even without the spam that would absolutely happen without content ranking.
Spam will happen on large platforms, and thankfully ActivityPub gives instances the ability to defederate/federate however they like to deal with problem instances. Personally, if Lemmy were to get rid of voting, there is no chance that I would use Lemmy whatsoever, and I feel pretty confident that most users wouldn’t either.
“Legit” instances are able to moderate/control the spam coming from their users.