I think you’re looking at two different things and treating them as one issue.
Nether Precision is perfectly fine talent. It adds some much needed spice to our otherwise bland rotation (which, historically, was basically “cast one spell forever”). It is very clearly a core mechanic of the spec now, and I doubt they’re going to be removing it.
The real problem is that Arcane Missiles are severely undertuned. We need to cast them to get the Nether Precision buff, but we don’t want to complete them because they don’t do enough damage.
Nether Precision sets up the problem, but is itself not the problem. It looks to me like Blizzard tried to fix the issue with Arcane Debilitation, but it just doesn’t quite reach the levels we would need. In order to fix the “unintended playstyle” that is clipping Arcane Missiles, Blizzard either needs to increase the damage that missiles does or incentivize us more to complete the channel (Blizzard, if you read this, please note that I said “incentivize us more to complete the channel” and not “disincentivize us more to not complete the channel.” There’s a big difference between the two).
Getting back to the topic at hand, if you’re testing this out in the real world (as in, not on dummies), make sure that both test cases are identical. One potential issue is if the mob you’re attacking is below 35% health, triggering Arcane Bombardment. If it is, that case is going to be doing 130% more damage.
Personally, I haven’t quite figured out which method I prefer. I’m sure there are number crunchers who can answer that (i.e. the guides) but there’s also a difference between damage and feel - sometimes I absolutely go with the style that feels better if it’s not going to be a huge difference in damage.
If all the damage multipliers on Barrage are additive (as in, the all add together for one total sum) and none are multiplicative (as in, add all the additives together and THEN multiply by the multiplicative), some napkin math at a glance to me looks like it could be beneficial to weave in some missiles when the target is above 35% health, but NOT beneficial to do so when they’re below the threshold. But that also makes some assumptions on how our damage amplifiers work - something I could be extremely wrong about.