You hit the right point: sparse content is the enemy of the subscription.
If you keep your content focused/niche enough I think overtime you should have a nice following.
I would love to discuss the problems with your two blogs, I'm actually trying to solve them.
I've 2 niche blogs and tried several ways of monetisation along the years. I only kept a direct ad (that adblocks can't detect) and amazon affiliates. I ditched Adsense (from 50€ it dropped to 1€/month) and tried donations (patreon, buymeacoffee, paypal) but it's not the right niche for that (art students).