I hear ya.
It sounds like you have no damage from the low oil issue... yet. Maybe add oil to protect the motor if you haven't already, but get the oil changed as soon as you can and ask them how in the heck can this happen to a brand-new vehicle. There are only a couple of explanations. If it's "burning oil", then there is a leak somewhere internally or externally to lose oil Or, they didn't fill the oil to the proper level when they did the PDI. A turbo motor does use oil quicker, but 2.5 quarts seems excessive. It can come low from the factory, that's why they do a PDI at the dealer. It also sounds like the wheel well liner issue hasn't damaged anything. So, if you have no damage yet, then pursue the liner issue with the manufacturer and try and get them to help you mitigate that through your factory warranty at your local dealership. I'm glad they looked at your motor and found the low oil. Have a chat with their service manager and maybe thank him for finding that. I'm sure you have already. Let him know what the original dealership said about your oil change interval. You may have done that, too. Then, let the service manager know that you'd like to service your car with them so close to you considering one never has to go back to the purchasing dealer for any kind of service. Loyalty to a dealer is earned and not automatic. Try and build a relationship with those guys and let them know to just shoot straight with you. That's all anyone can ask for. Finding good mechanics that stay at dealerships in these times can be difficult, so dealers are burning through new hires and just trying to find enough employees to handle the load.
I live in a semi-remote location, too. I purchase my Blazer at a dealer that is an hour and a half from me, so I made the choice to use the closest dealer to me 30 minutes away to have it serviced. I went in to have my passenger side seat cover replaced due to a cut in the red piping across the seat panel. It was a factory defect and the dealer made good to replace it under the factory warranty. When they fixed the seat, they scratched the B Pillar (the plastic trim between the two passenger side doors, one panel on my console at the passenger's feet, and the passenger side door panel. All of that was replaced under the factory warranty. I haven't even had my first oil change, which is free, and they just spent a small fortune replacing all these interior pieces because of an inattentive technician that was sloppy. It was actually quite comical. They had to pull the seat out to replace that seat cover and as he pulled it out, one of the tracks that bolt the seat to the floorboard dug into all those plastic pieces on the way out. What a mess.
My point in all that is, crap happens, but as long as they honor their word and get it all back to 100%, I'm good. I did have a come to Jesus conversation with my service advisor and his boss, the service manager. I told them that this was their only get-out-of-jail-free card. If anything happens again, I'm done with them. Well, I actually called my original purchasing dealer an hour and a half away and told them I'm going to bring my Blazer to them and have them service it. The dealer I purchased my Blazer from is part of a dealer group called Cavender. They have a very good reputation and I feel very good about them. I have purchased from them in the past and always have had very good experiences with them. I know a couple of the brothers in the family that are dealer principles/owners in the group and I just should have gone to them in the first place. I based my decision though on logistics and went to the closest Chevy dealer to me. Not always the best choice, but sometimes it works.
Approach your choice of dealer with the relationship in mind and build on that. Dealers aren't perfect and it is a business, so be patient when you can, but don't take crap either. I'm sorry this was so long, but I wanted to reassure you that you're not alone in your journey with your problems. Places like this forum are good places to share your victories and your defeats. We all learn from them, and there are times we can get help by speaking up.
Let us know how it all turns out. Inquiring minds want to know... lol.