I think you're correct, but I fished a Steffen 4/5 all day today with a DT5, and it was just great. In addition to the DT/WF matching, I think there's a fishing-distance criterion associated with loading and feel with a short line. I fish inside of 40' virtually all the time, and so might fish the heavier line, as I do with a few of my rods with dual designations.

I don't know, but judging from rods I've used in the past the rod markings indicate the line best used for 70' casts and a weight or two heavier works better up close. My understanding is that the first 30' of WF = 30' of DT = 30' of L +/- a few grains.
Pretty much in line with Brockton's comment.
But there is the bug in the back of my that a 4/5 is actually a 4 1/2 & 5/6 is really a 5 1/2 wt...Then there is the wide variance in line weight from brand to brand; maybe I'd just try a few and see what that rod likes with my stroke length.

For rods rated for dual line weights, I almost always use the heavier one. Though it's typically a DT. I had a Steffen 8.5 5/6 for a while that I liked best with a DT6.

Maybe I'm misreading the original question, but I think the answer may be that no, you can't assume that a poster's reference like "better as a 4 wt" means a WF 4 wt. If the poster says he used a WF 4 when deciding on that preference, OK, but even then, what brand/model; some are half or more line weight heavy. Then there's issues of natural conditions, intended distance, presentation, flies, my stroke vs. yours, etc.

Not trying to make it overly complicated. The simple thing is that it's all just a recommendation, or reporting information from experience; even the rod maker's suggested line weight is just that, a suggested starting point. After all, if they say, in their most definitive voice, "this is a 6wt rod," that means nothing to me if for MY fishing, it's perfect with a DT7 or WF4. Or I guess it could mean that I miss out on perfection because I didn't want to explore beyond the maker's "true" line weight. The type of comments you've seen are just aids to help identify YOUR preferred line weight.

need to remember that for the first 30' of line, there is no distinction between DT and WF with most manufacturers.
so unless you are regularly fishing at distances of greater than 40' (30' line + 10' leader) then it won't matter.

Sounds good to me.

but with a WF line, you're forced to shoot at the end of the belly.
With a DT line, you can keep much more "belly" in the air with the fly rod, because you can keep turning it over.

This has been well covered. I used to have the DT/WF opinion when I started out years ago, but I have since been enlightened. And this site has some of the best explanations to that end. Like others have indicated, for casting distance I will use the lighter line...either WF or DT. For in close, or when using buggier flies, or when experiencing windy conditions, I will use the heavier line. With that said, the heavier line is usually the preferred choice for most of my fishing.