Every decision he made was foolish and cost the lives of a lot of his own crew, including Morgan Elsbeth, not to mention the costs he repeatedly paid in equipment and weaponry - all of which were in short supply. He made unforced error after unforced error, and not one of his plans actually succeeded. But the geniuses writing the show handwaved all that stupidity away by having Thrawn say a few lines about how the losses were acceptable and everything was exactly as intended (even though what he said he wanted to accomplish before the failures and after were often totally different, and most of his plans were blatantly bad ways to achieve his goals to begin with). Anyone with a little bit of common sense could probably see innumerable better options.
But the dimwitted "fans" in these groups bend over backward inventing excuses and head canons trying to square the circle. They need Thrawn to be a genius because they can't admit that Filoni might not be that good a writer, so they ignore his obviously poor tactics and say that "Well, it all worked in the end, so he must have been smart!" as if the reason Thrawn completed his mission in the show wasn't purely because the plot demanded it and not because the writing earned his victory.
Stop making excuses for crap.