You're basing your opinion of a manufacture on bad advice, a used and possibly abused product with questionable history and some misinformation.I hate Subaru.
As for the AT tires, it's not the vehicle that is limiting you in your choices but the wheel size. ....and even then, I quickly looked up AT options and found these for 16x6.5 wheels (which are standard on the 2011 2.5x) on the America's Tire site:
ALL TERRAIN T/A KO2
LT215 /65 R16 103S D1 BSW
215 /65 R16 102T XL BSW
GEOLANDAR A/T G015
215 /65 R16 98H SL BSW
215 /65 R16 98T SL BSW
WILDPEAK A/T TRAIL
215 /65 R16 102H XL RBL
As for the fluids, there's where some of the misinformation comes in as pointed out. Personally, I do use the OEM coolant and conditioner. The coolant I can get for around $25 USD per gallon and the conditioner is only $5 USD. .....although about double the price of regular OTC coolant, hardly a huge ripoff IMO. $50 will get you two gallon bottles which enough for a full replacement with some left over for topping off from evaporation for many months or years to come. ....but again, if that's still stupid expensive, then you can use other popular brands as long as they meet the specs as mentioned.
Regarding parts, I haven't ever run into an issue where I couldn't source a part for my Subarus except perhaps the driver's side mirror matched in TGM paint on my wife's '08 Forester she broke when backing out of the garage. .....but thanks to the help of a Subaru parts vendor, she was able to locate one that was left in their network of sources which was great so I could just bolt it on rather than worrying about having it painted to match.
Also, just because your dealer you're interacting with is allegedly dishonest doesn't mean they all are. ....but even so, it pays to do your own research and find vendors, sources, etc. that you can use to check facts, gain knowledge, get advice from, etc. SF.org is really good start.
Two things I can agree with you on are the oil consumption (although your "gallons between changes" is grossly exaggerated) and the mileage (in my own experience). However, on the latter, I always get worse than advertised mileage in vehicles simply because of how I drive and in Subarus, I take into account the heavy, AWD drivetrain and full time engagement. In your case, your vehicle isn't anywhere close to an optimal state so there's that too.
As far as oil consumption, both my '03 WRX and my wife's '08 consumed oil. Her '99 Civic before it never ate a drop. Even my Challenger ate oil since new. .....not in "gallons" though. Just a quart or two between changes which for me are usually by the book (not every 3k miles). ....and btw, my wife's Forester has 253,000 miles on it currently as it slips into retirement as a "around town" vehicle for a family member. No more long commutes for this one.
Sorry you're having troubles with what is obviously a vehicle with a questionable history and sold to you by a deceptive previous owner. I'm also sorry about some of the misleading advice you've been getting from some of the mechanics you've dealt with. ......but I wouldn't judge a brand by this experience. In all honesty, this is why I always buy new and rarely buy used unless I am absolutely certain of the previous history which limits those purchases from friends, family or trusted sources where I have a trail. ....but that's just me. We keep our vehicles 10+ years usually.
In any case, I wish you luck and hope you can find a solution that works for you either to help you repair and keep the vehicle or get rid of it.