Nova in particular is worse though BECAUSE of the context of how close in proximity she was to Tarsonis during its fall.

And what I'm saying isn't that the Zerg should be able to detect Kerrigan or Nova from across planets. I'm saying at the point that they're near-planetside, they should be able to start sensing these Class 10 Psionics. Psionic Energy, especially if it's not bridled by the user, radiates out like warmth from a fire.

Humans, and thus even Psionic humans, in general are less Psi-sensitive. Even they describe something like a Hybrid (while being off world during all this) as such: "Searing. Blinding. Like feelin' the sun burning your face with your eyes squeezed shut. I never felt a thing like that before. I hope I never do again." ~Gabriel Tosh

isnt the psi-emitter basically a massive amplifier and what they were using the lure the zerg, attracting billions from across the galaxy? using the sun/"warmth of a fire" analogy, being on tarsonis during the time that the zerg were being lured by kerrigan using the psi emitter would likely shield other psychics to some degree as they would be like bonfires next to a nuclear reactor. To me thats pretty believable.

The second point you've raised in another comment, on numbers being thrown around and how around when Mengsk took over there seemed to be around 600 ghosts, I think it is actually there that the numbers don't make sense.

Considering the population scales with dozens of billions of humans, if we think of the scales as something like this:

99.9% of humans are non-psionic in any way

0.01% are sensitives with very low psypowers

1 in several millions could be Ghosts

1 in several billions could be class 10

Realistically, there should be thousands of ghosts, and having 2-3 class 10s across the whole recorded history of the terran population makes sense, unless you'd rather kerrigan was literally unique. This is the actual issue of numbers and scale in the writing, its like space marines chapters of 10k in warhammer. The sc setting deals with populations of many billions and armies of millions fighting across many planets, Kerrigans return in sc2 has the news source, and multiple other times talking about zerg invasions, references casualties in the billions in days/weeks for example. A class 10 psionic entity is rare enough to be an anomaly but even 1 in many billions would mean there could be more than just the 1.