The adjuster and the body shop people said that "fixing" the frame while possible would not be authorized as a valid repair by Ford and therefore by the insurance company. The only option would be a new frame and a new after market tow package, plus all the other misc. repairs.
In the not too distant past - say 2012, fixing a rear ended '11 Ranger would have been consider required. So, Ford had a repair guide on how to separate the frame sections and replace just the back 1/2. (I have a copy squirreled away somewhere that I could find the document number if you really want it; all '98+ Rangers have 2 piece frame).
Note: If the front 1/2 of the frame is "tweaked" you are looking at full frame replacement. I'm shocked that body shop could move cab/engine/transmission/axles/etc from one frame to another for $2.5k. (I've done it and know how much work it is.)
What people are asking for similar Rangers is probably about 10-15% more than what they sell for (everyone negotiates). KBB for SC XLT 4wd starts at $8.5k for '11 from what I can see online. Tonneau covers, stereo aren't included in std insurance - which is why I pay extra - I can't walk away from the 331 in my Ranger.
Most body shops quote purchase of all new parts; "finding & fixing" old parts just isn't worth it to them.
If you really like your truck/can't afford a '19; most places give you option to buy back your truck after insurance payout. Then you have repair your truck (either yourself or work with shop), have it inspected that repairs have been completed satisfactorily.* After which you can put your truck back on the road.
Unfortunately, it will be deemed salvage and only considered worth about 1/2 as much.
*Repairs will include making sure tires have adequate tread, brakes minimum depth, all lights work, no check engine, etc. Everything will be inspected as part of a salvage review.
Good luck