I have been told by the devs that is not keyed to rank its keyed to the mission. I think it should be keyed to my rank and not what mission I have taken.
AI are now factored based on combat rank versus other ranks. I can't quite recall the exact formula.
Elite missions theoretically should generate elite ships, but this has proven to be problematic, because not-elite commanders can elect to take them and the developer thoughtfully removed the natural gating this provided, without actually considering that 'Elite' combat ranking is entirely meaningless, or that sending Elite ships after 'harmless' commanders is going to potentially end in a bad time.
AI should actually be based on system security, mission rank, player status (eg: wanted) cargo type (eg: illicit) and other Faction and or BGS related factors. Because these are all actually predictable, and commanders can effectively gate their own experience, based on where they are and what they do.
Unfortunately this probably also requires commanders actively think and actively consider threat levels; which seems to be an ongoing problem, so commander rank as a key driver continues to be the outcome. It's also likely programatically more expensive than simply triggered on mission rank and commander rank. Less values to process for each encounter or some such.
This necessarily means genuine threat cannot exist. Because it's ultimately gated by a meaningless statistic. So for some the AI will be hopeless, others, considerably difficult. It will be very difficult to find a 'middle' ground whilst a meaningless statistic continues to be a major input factor. We have already seen what happens when the difficulty curve spikes.
And unless frontier decides to more adequately account for varying competencies by using the factors I have mentioned above to give commanders better control of situations, Thargoids
are going to be a disappointment for a great many.