I only watched the episode once so
correct me if I'm wrong but did Thrawn indicate that he had completely "neglected" any effort to find Ezra from the moment they arrived on the planet? I thought he just said he didn't know where he was without any specifics as to what effort had been made to find him. And with such a vague explanation of what's been going on all that time I'm fine with giving Thrawn the benefit of the doubt that he didn't do anything "stupid" in all that time with regard to Ezra. I say that because I don't have any problem coming up with a pretty big number of reasons that Ezra would still be alive and well with Thrawn not too concerned.
For one we can reasonably assume that in all the long years they've been there Ezra has done absolutely nothing to in any way inconvenience Thrawn. That's a pretty good winning streak of Thrawn being "right" in claiming that Ezra is no threat. Sure that can indicate that Thrawn has some level of arrogance (how could he not) that can even be considered a "flaw" that will bite him in the ass when Ezra causes trouble either this week or next week but, again, Thrawn was right for a
long time and I'd say there's more than enough wiggle room presented at least so far to allow for the Ezra/McClane of the story to come back and defeat the bad guy without the Hans Gruber of the story being lame.
Of course this is still Disney+ SW we're talking about so I fully realize that we're potentially only one episode away from a big flashback episode that shows Thrawn chasing Ezra at a slow jog across the tundra, never closing the gap due to Ezra's undefeatable serpentine Benny Hill maneuvers.
I actually like the notion that the blind spot for the Empire was so easy to exploit for anyone who doesn't approach the locals with guns blazing. To me that's very much in the tradition of classic SW themes.