I think you're looking at how AE works from the wrong angle (also some of the numbers are a little off since if you're assuming HT buff is up then you need to apply it to HT-RoT). You might get slightly higher damage for your TP from single target abilities, but you're only applying that damage to a single mob. For example, take a fully buffed set of single target moves, and compare those to a buffed AE moveset.
HT must be refreshed if down, and DE must be applied to each mob, so you'd get this:
170+198+242+181+242+363
HT buffed HT-RoT gives a potency of:
170-165 followed by 187-165
We'll consider a pack of 3 mobs, each of which requires 1000 potency to kill. With Full Thrust the process would look like this:
HT-ID-Dis-TT-VT *switch* FT-ID-Dis-HT *switch* ID-Dis-TT-VT-FT *done*
170+198+242+181+242=1033 *mob 1 dies* 330+198+242+187=957 *mob 2 dies* 198+242+181+242+363=1226 *mob 3 dies*
Give or take some autoattack damage (such as on mob #2 which I cut at 957 cause an autoattack would make up the difference), it'll take somewhere around 12-14 GCDs to kill all 3.
With HT-RoT it looks like this (M1=mob 1):
HT@M1-RoT | HT@M2-RoT | HT@M3-RoT | HT@M1-RoT | HT@M2 | ID-Dis@M3
170-165 | 187-165 | 187-165 | 187-165 *mob 1 dies* | 187 *mob 2 dies* | 198-242 *mob 3 dies*
Most of the mobs were dead after 9 GCDs, with two extra used to kill off the final mob with single target damage.
You might get slightly more damage for your TP on a single target, but the overall group damage is much lower and so everything will take longer to kill.