Yeah but it is still mass and volume that might reduce available payload?

Doesn't matter. The point is that, thanks to reusable boosters, launching satellite constellations, and other recent developments, space is becoming much cheaper - so if you can't fit 8 JWSTs in one Starship, just launch the rest on another, and it'll still come out cheaper than the original JWST.

Ultimately it becomes so cheap we'll be able to put workers up there to assemble and maintain the telescopes, just like on Earth. We might see telescopes in telescope farms near a small station for the workers. It might even be possible to send workers out to the Sun-Earth L2 point to maintain telescopes there.

For what it’s worth, people have already fixed telescopes in space (ISS astronauts operating on Hubble).

Shuttle astronauts. ISS and Hubble are in very different orbits.

Totally, I mixed up my spacewalk associations, thanks.

Not really. Starship is aiming for 150 MT to LEO. The launch mass of JSWT was 6.5 MT.

Yes, JSWT was launched into a L2 transfer orbit and not LEO, but from the above margins there is probably enough spare capacity for this.