You never ever have a reason to use DTC, unless you simply don't own the ITU hull mod.
Which is exactly the point. DTC is a stand-in.
Aside from that, I'm not sure I really agree that extended range is that necessary. It's good for a standoff playstyle that takes forever, but not all that helpful for a direct assault playstyle intended to rush down enemy targets as quickly as possible, which is how I play. I use it sometimes, but not always. In fact I'd consider Unstable Injector, which is almost exact opposite of ITU/DTC, to be the more mandatory hull mod in most cases.
On frigates, DEs - sure. Cruisers/Capitals are just never fast enough to face hug enemies, unless SO. And a ITU/DTC-less cruiser often has less effective range than DE, since it's large itself and many slots are not on the very front of it.
ITU gets more efficient with size, UI - less. UI is mandatory for frigates (except maybe opticc Wolf of Tempest), good for DEs (but less so for AI piloted ones), dubious for cruisers (on Eagle/Falcon or Aurora UI doesn't even increase your average speed that much, since a lot of it comes from ship system). Paragon, Conquest and Odyssey can consider UI, but I still find more range better for them.
In terms of percent speed bonus, UI gets more efficient with size. A Tempest with 180 base speed gets +25, which amounts to a 13.8% gain at the cost of 10% of its OP. A Paragon with 30 base speed gets +15, which is a 50% boost at the cost of 6.8% of its OP. So in percentage terms, UI is over 5 times as efficient on a Paragon as on a Tempest.
I pretty much always run UI on my Paragon. Coupled with aggressive use of zero flux boosts, I can chase down most cruisers and destroyers (the enemy will never have 0 flux boost unless they are in full retreat). When I'm fighting Remnants in particular I like to hold fire until I can touch shields with the Radiant, then let loose. Even after it teleports away, I have enough speed and range (range does matter, it's a question of how much) to keep up and kill it.
Even if I can't fully outspeed something, more speed relative to their speed means that I can push forward and hold them in firing range for longer. That's how you end up killing cruisers and destroyers, especially faster ones like Falcons, with the Paragon, where otherwise they would simply run away as soon as their shield gets low and never take real damage. Get as close to them as possible before they get scared, and then have as much speed as possible to chase after them while they try to turn and run. You won't beat them in speed, but it means extra time to do damage.