Well first realistically you won't get 13.5 or 10 years out of your LEDs as we already agreed. The same unrealistic numbers are given to both halides and T5s and previously discussed. Second how does your bulb and energy savings compare if you have to replace your fixture every six years compared to simply changing bulbs every year?
The other advantage to T5s that people tend to forget is the ability to setup a kind of bulb replacement rotation. Basically only replacing 2 out of 8 bulbs every six months, every time replacing a different set. This keeps your light levels more consistent eliminating the need to lift and lower fixtures and shocking corals. It also means you're only placing half your bulbs every year which saves you significant money in bulb changes.
The most common argument to go with LEDs is to actually save money in the long run which I think you LED guys should stop using and push more on the lower heat and more defined spectrum (if that really is an advantage).
If you're LED fixture costs $2000 and lasts say 6 years and uses around 250W which means it'll cost around $110 per year for power. If you have to replace your fixture every six years then after
10 years (if you keep it that long) it'll have cost you around
$5100.
Now if you compare that to say a 500W halide system which can be purchased for around $1000 (equal quality) and will cost around $220 per year to run for power and around $140 per year for bulbs. After
10 years (again if you keep it that long) that adds up to
$4600.
Both realistically are comparable in basic cost however neither include premature failure which is possible for both options however the halide system would offer a cheaper fix. Also after 10 years you only have 2 years left on your second LED fixture and if at some point you decided to sell your fixture for whatever reason the halide system will no doubt return a larger percentage of your investment. And I know that you can argue that you build your own fixture so it was cheaper and you can replace LEDs easily and blah blah blah but what about the rest of us who don't want to or can't build such things, I call this the real world
as at least 90% of people in the hobby don't want to build there own light fixture.