yeah i don't get why 'strawmanning' Y is necessarily bad in this case. You also automatically strawman your own position, so what? that's kind of the point, to entertain another theory, possibly one by one.
"Steelmanning" doesn't involve strawmanning any position, unless the position you're "steelmanning" is inherently dependent on a fallacy—specifically, a fallacious strawman version of some other position. If you can find a non-fallacious argument for a proposition, you have to use it instead if you're "steelmanning."
So I don't agree that "steelmanning" involves strawmanning some other position Y, except in the most extreme cases, in which the position you're "steelmanning" can be trivially dismissed. Most positions that people actually hold have some valid argument in their favor, and therefore are not necessarily dependent on strawmanning other positions.
If you're simply repeating what the other person said, you're not using the concept to full effect.
If you're framing your own argument as a strawman instead of clarifying the opposing argument, you've missed the plot entirely (unless your opponent is arguing for the use of strawmen in debate?)
The utility of steelmanning is to minimize assumptions. Everyone has to demonstrate their comprehension. You can take it further and in order to 'pass' the steelman stage, you have to agree with your opponent's steelman argument, or have a dialog to refine it until you're satisfied that both of you understand your argument.