I follow your logic, but frankly the suspension of my disbelief is pretty easily kept up with the explanation that Mando brought a human element of unpredictability to his fight with Ahsoka, and that she very quickly let up, whereas the dark troopers aren't particularly bright AI and Mando had trouble with one because of its overwhelming physical strength and resistance to blaster damage. It's maybe a bit of hand-waving, but I think Ahsoka and Luke are wont to show some restraint when dealing with people, and much less so when dispatching big dumb robots.
Similarly I noticed some comments saying, "Hey, what happened to Bo-Katan's other minion—the dude? Was he not present because it was an excuse to show a Girl Power™ moment?" I didn't see the need to read into it any further than "We're catching up with these characters after some time; Bo-Katan probably sent the other guy off on his own following a different lead to Gideon."
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