Would spamming low effort comments to fill a quota then fall under the spam bit, not necessarily self promotion bit?

Possibly, but there’s equally gray area that what counts as low effort spamming and what actually contributes to the conversation. For example I’ve replied to comments “I’m using X to do Y” with “I’m using X too and I’m happy with it” to give an opinion to possible solutions. That kind of comments are easy enough to throw out and, if the “10% rule” is interpreted strictly, it isn’t really obvious if they should be considered as “improving your ratio” or as a part of actual conversation.