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Yes that generalisation is fine.
The important thing here is f ratio, and a barlow simply multiplies that out to an easier number for eyepieces to handle.
When I first got into astronomy, f6 was considered as fast as one would consider for a newtonian and most scopes were f8. That meant that coma was not an issue, particularly with the unsophisticated eyepieces that were used. Today there is plenty of exotic glass about and short focal length mirrors being produced; but simple physics demands that the more you push it, the deeper you will have to delve into your wallet to overcome the next layer of problems.
I use a paracor about 50% of the time on my f5 dob and I think it is an absolute must have if you are using an ultra wide f.o.v. eyepiece.
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