In general, I agree. Being an advanced being isn’t auto win. If your average newly metamorphosed 21st or 22nd level avangion or dragon, or newly transforming cleric elemental, just walks in (or is caught in a situation where they can’t afford to just teleport away and come back later, like Kalak was) they can totally be overwhelmed by decently powerful but definitely non-advanced/non-epic foes.
The kreen have somewhat of a disadvantage compared to a comparable group of humanoids since they don’t have arcane magic and have basically no knowledge of it, but it’s not an insurmountable one if they’re willing to accept losses - at least if a dragon/avangion decides to stand and fight. Hit and run tactics are more questionable… I think a smart wizard with 9th level spells and the resources to make magic items can become essentially unfindable with the resources they’d have.
But the Dragon is far more powerful than a starter advanced being, and Valley of Dust and Fire claims he has all these contingencies and defenses etc. If that’s true, I don’t think the kreen could do anything to hurt him longer than it takes to regenerate PSPs and HP after he teleports away.
OTOH, the Dragon as shown in the Prism Pentad novels apparently doesn’t have any of that; he doesn’t fight smart, doesn’t teleport in and out, and doesn’t have contingencies whisk him away when he’s in real danger. So it depends on which you take as more canon…
But more importantly, this all assumes that there’s an open fight … That the advanced being’s enemies know the advanced being is an enemy. The sorcerer-kings and the Dragon have the time, psionics, and magic to rig the situation so that isn’t the case. While Ivory Triangle disagrees, it seems pretty clear in the Prism Pentad that the Dragon’s Levy isn’t a generally known thing. For kreen it would have to be a bit different, given that they don’t practice slavery, but if the normal base rate of hunting parties not coming back ticks up somewhat… All you have to do is mind control a leader and get them to come to you…
(Thri-kreen of Athas says that there can be up to 30 eggs in a clutch. Even if that’s an extreme and the average is more like 15, their mortality rate has to be colossal for the situation to be remotely stable. I think life expectancy would end up being something ridiculously low.)