You could use tubeless without sealant, but it'd be quite a gamble. But yeah TR is essentially a bit of a half-way house requiring more than regular amounts of sealant, which might be useful in the longer term. IDK.
No ones does though, right? Which is why most tyres are TLR. No point having added weight and rolling resistance when everyone is going to chuck in sealant anyway.
True, I'd forgotten my own experience of the air escaping through the sidewalls. I'm still trying to find the sweet spot of achieving a seal. Currently at 50ml and still not sealing.
You could use tubeless without sealant, but it'd be quite a gamble. But yeah TR is essentially a bit of a half-way house requiring more than regular amounts of sealant, which might be useful in the longer term. IDK.