Every single telescope out there is a compromise, as the benefits of one aspect will impair another. With regards to focal length, it is no secret that a longer focal length will produce a better image, in a refractor it will have less chromatic abberation, less field curvature, the list goes on. But manufacturers for the most part gravitate to shorter focal length refractors because the market dictates that these are more in demand due to being lighter, easier to mount, more transportable etc. Same with the ED glass the article mentions, it might be 18x worse with its thermal expansion number, but it's benefits are much improved CA performance, and most people will take the fringe free views. Having said that there is still a market for these long FL refractors, people seem to be passionate about them
