I propose a few ways of using these words.

"Instrumentally rational" = successful on account of being epistemically rational. Success for other reasons does not count.

"Epistemically rational" = correctly using observation and reasoning to arrive at true beliefs, and making the decisions and actions recommended by those beliefs.

"Irrational" = a privative concept, expressing not merely an absence of rationality, but an absence where presence is seen as having been possible.

How widely or narrowly you draw the line around "irrational" depends on how much of a counterfactual difference you are imagining being possible. Draw it widely enough, and sandstone is irrational for being so easily eroded by the wind. Narrowly enough, and everyone is perfectly rational all the time, in the same way that the Pentium III with the FDIV bug worked flawlessly. Somewhere in between there is a reasonable place to draw that line, but arguing over where to draw it is an argument about what to call things, not an argument about what properties those things have.

For the avoidance of doubt: I will happily agree that, all else being equal, being autistic is generally a disadvantage, and that this disadvantage is a matter of cognitive deficiencies and not only of (e.g.) prejudice on the part of others. I just don't think "irrationality" is at all a good way to describe that disadvantage.

I agree.