The argument for SSTOs was that staging was too scary. But experience since then shows this argument was bogus. Staging can be made highly reliable.

Even a small amount of delta V provided by a first stage makes the job of the "almost SSTO" second stage much easier. And a low delta V first stage can be rugged, with high high safety factors, and is easy to recover at the launch site.

Put another way: if you have an SSTO, its payload increases dramatically if you stack it on a very low performance recoverable first stage.

I don't see any way SSTOs are going to be preferable to TSTOs, especially if the SSTO has to use hydrogen to get off the ground.

Against the cost of a lower payload fraction. Say you get 4% with TSTO, 2% with SSTO. And if you run into trouble with the design, the SSTO payload moves towards 0%. Your operational savings need to compensate for a doubling of cost per unit mass payload, possibly much more.

And even though full reusability is much easier with two stages, and has not been achieved yet.