The thing is, on-topicness is in the eye of the beholder, so it can't really be an objective metric, needs to be personalized 🤔
Discussion
You could maybe ask for follow recommends for X topic, ranked by WoT and SME.
Then you'd find new, high-quality material, even if they weren't in your WoT. Would be a way of getting out of WoT-bubbles.