I dont think stremio does either technically. Stremio it's typically used as a front end application for debrid services. Mainly real debrid, all debrid and premiumize.

I believe the 2 debrids only download, but i think premiumize seeds, but not 100% sure.

That being said if a file gets added to these services it is not constantly leeching like op said. The real debid servers for example will download a torrent and distrubute the downloaded file throughout their cdn, leaving it in their cache for 30 days. I believe each time it is accessed by a user that 30 day clock is reset.

Stremio typically only shows cached torrents in there app so in order for a user to force a download they would need to go to their debrid provider directly and add the torrent causing it to get added to the cache.

Is it bad for the torrenting network, yes because they don't seed, is stremio using up all of seeders bandwidth, probably not