T5HOs do work well in comparison to other fluorescent sources like CFLs, but you still need to replace lamps every 3-4 months and there is a maximum "throughput" you can get out of them. What I mean by that is that you can have a certain intensity that you can get, and you can't get past that. You can use top shelf reflectors, but those have a width requirement, and cramming the lamps closer cuts off reflection off the back of the lamps so you end up with diminishing returns as you move the lamps closer. Once you reach the maximum output point, then you are limited by photoperiod, and then your total light-energy per day is maxed at 24/7 operation.
LED on the other hand have a much better efficiency in terms of the output of useable light energy. Sometimes too much, at least at first. It is rather easy to find an LED fixture that will outperform T5HO in terms of intensity (rate) that you can cause photosaturation and get zero growth on a new screen. So you have to do things like splitting up the photoperiod, using a diffuser, dimming the fixture, or using only part of it, at least until the screen matures.
Then, depending on the system and scrubber, you can start ramping up the lighting and photoperiod. With LED you can get a much more intense output, which means (in many cases) that you can run a shorter photoperiod and get the same results as a T5HO runnning 18+ hrs/day. What that also means is that while your T5HO scrubber might be limited by hours in the day, your LED scrubber equivalent is not, at least not as much.
For instance, you could build a scrubber using the Expressions LTD LED strip light, which has a similar useable light signature compared to a T5HO (a 24" T5HO lamp has about 18" of useable linear light, the output near the ends of the lamps drops off sharply) and you could use one of these in place of a 2-lamp T5HO fixture. But, where you could only fit a 2 or maybe 3 lamp T5HO fixture in a given space, you can cram 4 of the Expressions strips in the same place, which is more equivalent to the output of 8 lamps.
These numbers I'm throwing out here are not proven and calculated by me, I'm just throwing that out there as an example to paint the picture of why it is wise to consider LED over T5HO, because there are many reasons outside of sheer price of lamps vs price of LED fixtures.