That's one person's opinion. From my experience, the bombs are much closer than people think. If you have Breath of Hydra or LotC then yeah you have to use Nether Tempest, but the fact remains the bombs still have strengths and weaknesses.
Like I said, in general I prefer Frost bomb on single target because the damage compared with NT is nearly identical. I['ve tested it on dummies and ran simcraft. What I gain is the ability to predict when my BF procs will happen, which fits with my playstyle. Other people may want the mobility offered by NT and don't mind the random nature of BF procs. For me, unless the fight requires tons of movement, the mobility advantage of NT doesn't outweigh the predictability of brain freeze.
But I've seen many posts, including the frost pve guide recently posted, saying all the other bombs are useless and you should always pick NT. I'm saying that Frost Bomb, and LB are more competitive than people give them credit for. And on single target, the difference is very little.
Uh.. What Lhivera said was about Multi-targets. Yes you are correct that on single target the Bombs are very close, but on multi-targets NT comes out way ahead unless all the adds are tightly packed together.
It seems like the theme for ToT is ADDS+MOVEMENT, loads of both. And the adds are all spread out, so Frost Bomb doesn't do well.
What Lhivera said is that before the 40% buffs, Frost and Living bomb were competitive because NT's DPE wasn't high enough for you to just cast it on every single add that was up. It was better to cast 1~2 NTs and then go back to your normal rotation. But with the 40% buff to all bombs, NT's DPE got way to high and it's better to just keep it up on all targets and only then worry about your normal rotation.
It's not really a case of 'personal opinion', it's numbers. The bomb buff increased NT's DPE value way too much, so on fights with adds it's clearly the best choice.