Not really too worried about La liga. Dumfries looks suited to the PL because he has lots of pace and the ability to go up and down the pitch. Pace and athleticism are the most important abilities for a full back these days. They don't have to be brilliant on the ball because they are not expected to always take the ball in tight spaces or play between the lines. Being able to attack space at pace is a key for a full back. They are usually the players with the most open space in front of them.
Aarons is a good player but I doubt we can afford him. I'm not convinced on either of the other names you mentioned. Dest in particular is very inexperienced and I've not seen much that I'm impressed by, although I have only watched him in a couple of CL matches.
The other positive with Dumfries is that he will be available as a wing back and I have a feeling we might see some 3 at the back.
Totally get where you are coming from with this actually
Holding your own in the Premier League requires you to be physically capable, probably above all else to be honest
La Liga is a completely different kettle of fish
You see it all the time where players come to England from the continent and find the pace and physicality of the game here a real issue
Dumfries strikes me as someone who would adapt quite easily on that front, and I think he's a solid player too
We could probably plug him right in, and considering we need to hit the ground running this season that's a BIG selling point IMO