I wouldn't mind having maybe twice the population and activity we have right now.

We don't need millions, but 100k would be a nice community, with enough people to discuss more niche topics, and more creators posting their work.

Reddit is still a much more diverse group than the Fediverse, which is still sadly dominated by technical people, mostly men, of a generally very similar political position.

Also Lemmy and other forum-like instance types are the closest alternative to Reddit on the Fediverse, so it makes sense to let people on Reddit know that there is a more open alternative.

Everyone on Lemmy used Reddit at some point. It's not like we're some rare breed of human.

Yes its called free speech they might be idiots or shit heads in your eyes but they have as much of a right to speak as u do.

Reddit has existed and thrived for nearly two decades without a usable search feature. Lol

Mods on /r/Denmark removed my post announcing the creation of Feddit.dk within minutes for self-promotion.

In some ways, I don't blame them too much. Most instances, including Feddit.dk, have rules against advertisements and self-promotion. It's kinda difficult to let people know that the Fediverse exists when we are so opposed to advertisements on a principal level (definitely not suggesting using ads, for the record).

We can basically only rely on mouth-to-mouth discovery and that's very slow.

Even communities can be tough.

/r/unixporn was closed for a while, the mods encouraged people to move to Lemmy, it was a failure

It is

Lemmy is growing and that’s all that matters

Not so much unfortunately, it's stagnant or in slight decline: https://lemmy.fediverse.observer/dailystats

Can someone buy ads for Lemmy on Reddit?

En masse*

I don't think the way to go is flooding them with garbage. What reasonable person would see that and think "Yeah, this is where I want to spend my time"? The only solution in my mind is to engage in meaningful, relevant, organic conversation, and talk about how Lemmy has been a great (or at least good enough) alternative to Reddit. Let the platform win on merit.