For some tasks, surveys in particular, field of view is critical. You would need many Hubble telescopes to do what Roman can do mapping everything out there.
"What really makes Roman stand out is that it is designed for wide-field imaging. The cameras on telescopes can often only detect objects in a very small patch of sky. If we use the size that the full moon appears in the sky as our guide, Hubble’s field of view is often smaller than that —meaning each picture it takes is of a patch of sky smaller than the full moon. Webb’s instruments often are even smaller than Hubble’s. Each picture taken by Roman, however, will be larger than the full moon, allowing it to survey more of the sky much faster than Hubble or Webb."
Hubble in certain circumstances can see narrow and far. If you express this as a cone, you can extrapolate a volume.
It might be very useful to have something that can search wide and maybe not as far; nearer Earth dangers perhaps. Express that as a wider cone and extrapolate volume.
The Rubble and NGR have the same size mirror but they are constructed differently. The former is not sharp over the entire field of view, the latter is - that coupled with a much, much larger camera (nearly 300MP) lets it record images at least equal to to HST but over a very wide field of view.
As to speed, it is not just the camera view that makes NGR faster but also physical factors such as not having to wait for earth to get out of the way.
"What really makes Roman stand out is that it is designed for wide-field imaging. The cameras on telescopes can often only detect objects in a very small patch of sky. If we use the size that the full moon appears in the sky as our guide, Hubble’s field of view is often smaller than that —meaning each picture it takes is of a patch of sky smaller than the full moon. Webb’s instruments often are even smaller than Hubble’s. Each picture taken by Roman, however, will be larger than the full moon, allowing it to survey more of the sky much faster than Hubble or Webb."
https://science.psu.edu/news/ask-expert-will-roman-help-reve...
https://science.nasa.gov/mission/hubble/science/universe-unc...
Those are galaxies. In a field of view "about 1/13th the diameter of the full Moon."
Hubble in certain circumstances can see narrow and far. If you express this as a cone, you can extrapolate a volume.
It might be very useful to have something that can search wide and maybe not as far; nearer Earth dangers perhaps. Express that as a wider cone and extrapolate volume.
As to speed, it is not just the camera view that makes NGR faster but also physical factors such as not having to wait for earth to get out of the way.