Telescope Reviews: Why?

There is focal ratio and there is focal ratio.
I.e., it depends how the f/ratio is produced.
An f/10 refractor and f/10 newtonian both have very flat fields and close to zero inherent astigmatism and coma in the lateral field (what little of it there is).
A catadioptric scope, however, does not have as flat a field, nor have its lateral field coma or astigmatism as well corrected.
Cats designed for refractor-like images are usually f/15 and longer, or employ complex correctors somewhere in the image train.

In this era of sub-f/4 scopes, I do notice that there seem to be a lot of TeleVue eyepieces being used. I don't think that's an accident. Designers of eyepieces can make the designs more complex (and expensive to produce) to handle the short light cones with their oblique rays, but most do not.

Telescopes started with singlet lenses and f/ratios of 30-100.
When doublets came around, telescopes got "short", f/15-f/25.
The first reflectors kept up with this, at f/10-f/20.
So eyepieces didn't have to be very complex or have steep curves on the lenses to correct the images.
Once scopes became f/6-f/8, eyepieces started showing aberrations they didn't have at longer f/ratios.

You see, every design has a "Critical F/Ratio" below which the off-axis rays start causing problems like astigmatism and lateral chromatic aberration and field curvature, etc.
If those CFRs were published for every design, a lot of manufacturers would make very few sales, so the CFRs are generally NOT published.

Here is what I have for CFRs for major eyepiece types:
Huygens f/12
Herschel f/12
Ramsden f/10
Kellner f/6
Plossl f/4
Nagler I and II f/4
Monocentric f/10 (f/5 for Steinheil design)
Abbe Orthoscopic f/6
Symmetrical f/6
Hastings triplet f/4
Konig I and II f/4
Erfle II f/4
RKE f/6
Galoc f/4
Zeiss Astroplanokular (Masuyama design also) f/4

It should be noted that that does not mean that every one of the above eyepieces with a CFR of f/4 performs equally at f/4. Many of the earlier designs were originally narrower fields and have been "stretched" to produce wider fields more popular today. So that means either that the critical f/ratios need to be lengthened or that the designs should not be stretched to such a wide field. A good example of this (and I can pick on it here because it is no longer in production or available) is the 5-element Plossl from Meade, called the "Series 5000 Super Plossl". At 60 degrees, this eyepiece had a lateral field filled with chromatic aberration, astigmatism, distortion (of both kinds!) and field curvature. Had the design been confined to 50 degrees, it might have been a truly good design for the amateur astronomer. At 60 degrees, though......
Even worse, a similar design was stretched to 65-70 degrees for many low-power eyepieces sold under a variety of labels. And sold with f/4-f/6 dobs. Tsk, tsk.

So, most eyepieces are designed to work well at or above certain f/ratios, and confined to an apparent field not larger than a certain angle. If you want to expand the apparent field, lower the critical f/ratio, or both, the eyepieces will have more lenses and generally be more expensive to design and manufacture.

As they say, Wide, Cheap, Good. Pick any two.