As long as these economics continue to hold they'd be stupid to discontinue the free tier.
Say 5% of the free tier users converts to a paying customer within 5 years. And user growth is constant. Then over time, you will get a much larger free tier user base, compared to your paying customers (in absolute numbers). At some point, it must become tempting to charge all free tier users a little bit to continue, because the group got so big, so there is a lot that can be earned there.
Is this wrong, or should we expect this?
This is one the the most fundamental components of SaaS accounting, it’s absolutely not a “wild guess”.
Welcome to economics.