I agree, to an extent.
But, what are you going to do when you've only got four bench spots, one of which is reserved for the backup catcher? Guys have to play multiple positions.
In reality...
Jeffers, Vazquez, Julien, Miranda, Correa, Buxton and Kepler (and likely Lewis) only play one position.
Farmer, Larnach, Margot and Martin have almost exclusively played two positions, with the latter three being two outfield spots. You could list Wallner as playing two spots when he was up, but he was really a LF who played some RF when Kepler was hurt.
Kirilloff has played two outfield spots and 1b, but half his starts have been in left. He's really a LF and backup 1B who played some RF when Kepler was hurt.
Castro is really the only person who has moved around a lot, splitting time between 3B, SS, LF and CF, but most of his starts at 3B, SS and CF have been as an injury replacement. The intent wasn't for him to play much at any of those three spots, but fortunately, he's been able to.
In terms of the minors, I suspect you're especially referring to Martin.
In 2021, it looks like Toronto was trying to decide whether he was a SS or CF, since he split time evenly. The Twins did the same after they acquired him.
In 2022, the Twins tried to focus on SS. with 70 games at SS and 9 in the OF. That was at a time when they didn't have Correa signed for the future and Lewis was injured most of the year.
In 2023, they had Correa signed long-term and they decided Martin wasn't a shortstop. They slid him down the defensive spectrum in terms of the infield to play half his games at 2B, which makes sense when you are thinking you may trade/non-tender Polanco and you aren't sure whether Julien is the long-term answer. But you hope Julien is the answer and you also have Lee and Miranda in addition to Lewis, so you use him the outfield. In the outfield, he split time between LF and CF, but that makes sense when you aren't sure how many games you're going to get from Buxton. You hope Martin doesn't have to play CF in the majors, but you want to be covered in case you need him there. And if you don't need him in CF because Buxton is healthy and you have Castro as the backup, then you want to get Martin some time in LF in case that's the only spot available.
In 2024, from what we've seen, they've given up on him as an infielder. He's played both CF and LF, but his CF starts were mostly as backup to Castro when Buxton was out or as backup to Buxton when Castro was needed at SS for Correa. At best, Martin was intended to be the third string CF. In actuality, they wanted him to be fourth string, after Margot as well, but that hasn't happened.
So yeah, they haven't committed to him playing a specific spot, but they almost couldn't. Had they done so and guessed wrong, they aren't covered in another spot. And with such a short bench, every team is going to need a Castro, so it makes sense to try grooming someone for that role. (Said another way, if Castro goes down, who gets his multi-position role?)
I've only heard the radio and read the TD versions of Martin. I haven't seen him like you have. Frankly, it seems like he's never going to hit enough to be a regular, so focusing on one position wouldn't have been helpful unless he's going to be a Gold Glover. I don't think he was ever seen as that, even if he focused on one spot. Instead, being a utility guy is his most likely opportunity for success.
But from what I've heard and seen, I'm not sure that's even realistic. I assume the Twins are intending for the Lewis/Julien/Lee/Kirilloff/Larnach/Wallner group to make Martin irrelevant. Unfortunately, they haven't done that yet and injuries have happened, so we've been stuck with more Martin than intended/hoped for.
I hope we don't see any more of Martin. That's not because I have anything against him, I just hope that guys stay reasonably healthy and perform even at the midrange of their expectations. If they do, I don't see a spot for Martin. Even at his best, he seems like a Niko Goodrum.
(Sorry -- that got much longer than intended.)