if you have a more effective metric in mind, I’d love to hear it instead of just pointing out flaws

I mean, isn't the whole point of this comment section to discuss the merits and flaws of the proposal you've made? If we're not discussing the downsides, too, what's even the point?

That said, an ideal system would be a measure of the quality of content, not the quantity of content so, as another user has suggested, some measure involving net upvotes might be more effective. Yes, obviously a user can create multiple accounts to upvote everything and fuck with that metric, but I kind of doubt many folks would go to the trouble.

Maybe some combination of PCM and the average number of votes divided by the number of active users could generate some sort of quality metric. At the very least it might be a measure of engagement.

Creating a bunch of accounts possibly to manipulate votes

Looking from the admin level, doesn't happen that often. Vote manipulation is already something we keep an eye out for, and usually it's done to highlight certain content (ex. pushing some political angle) rather than boosting one community over another.

you can stop seeing by adjusting your "Show Bot Accounts" setting

I like some bots, but I only subscribe to a bot-only community if the volume of posts is reasonable.