That's not how this works. The JWST was limited by the size of its faring, but increasing the size of the faring doesn't mean they'd ship a less complex telescope with the same functionality; they'd ship an equally-complex telescope with more functionality. Better for science, yes, but that doesn't translate to more expenditure that could be captured by the launch company. And that still relies on a government that gives a damn about funding science, which is not not the direction that the US is heading in.
reply> that doesn't translate to more expenditure that could be captured by the launch company.
replyOf course it does. With Starship, SpaceX could've charged NASA/ESA more to launch a bigger JWST than the cost to launch with Ariane 5, with huge profit margins.
On top of that, with a much larger fairing, you could almost certainly simplify the telescope and increase capability. A significant part of the JWST's complexity is the unfolding sequence, which could be simplified with a fairing that is more than double (triple? quadruple?) the volume.