Is it true that, for example a 4wt DT line would be the same as a 5wt WF line? If a DT line is heavier in total weight when you get past 30ft, it should be like casting a WF line one weight up? Right? Am I getting this, or am I way off?
If I am correct, than a fly rod that is rated a 4/5 wt would be to use a 4wt DT or use a 5wt WF. If I am wrong, that will be a sign for me to give up on trying to understand lines. Because in all reality, I don’t.
Maybe yes, maybe no. Traditionally the advice was as you said – when a rod was marked 4/5 it meant the mfr recommended that you use a DT4 or a WF5. But not all modern WF’s are created equal – some are now 1/2 or even a whole size heavy, some have short, fat heads, some have long front and/or rear tapers, etc.
Your confusion is warranted, Scotty. I believe the line mfr’s are sincerely trying to make unique lines that suit every customer, but that requires a nearby, well-stocked brick-and-mortar shop with several demo lines ready for that customer to test cast. And don’t get me started on how casting on a lawn or parking lot isn’t the same as fishing, so its usefulness in evaluating a given rod/line combination is limited.