I agree, it makes no sense, especially when the 4Runner has the wiring, but is rated to tow less. Any competent trailer shop should be able to install a controller, but sounds like your Bluetooth unit is working well for you.
You can wire in your p3 with the generic harness it came with.
https://www.tacoma4g.com/forum/threads/brake-controller-harness-install-diy-how-to-instructions.6777/
Have you read this thread? The wires are not there. Did you read the other thread? The 4R manual shows a prewire. The Tacoma manual does not. This information is readily available. There is a write up on how to install one floating around.
No need to pay hundreds
https://www.amazon.com/dp/B0DT43Z37F?ref=cm_sw_r_cso_cp_ud_dp_91M6JD7TEACC06E67W3F&ref_=cm_sw_r_cso_cp_ud_dp_91M6JD7TEACC06E67W3F&social_share=cm_sw_r_cso_cp_ud_dp_91M6JD7TEACC06E67W3F
The truck has a 3 gallon reserve that is not calculated in the distance to empty. It is capable of great fuel efficiency if you keep your foot out of it. I’m currently at 20mpg with mostly city. I’ve had a tank of all highway in the mid 20s.
They will probably do like what a lot of other manufacturers are doing and put an oil level reading in the multimedia. Audi has not had an oil dipstick for almost 20 years.
Any competent trailer shop should be able to accomplish this. There was a time when pnp brake controls were not a thing. With the new Bluetooth controllers, you don’t even need to do that.
You don’t need a pre wired brake control. The Prodigy P3 comes with a generic harness. I think it’s BS the Tacoma isn’t prewired, but you could have used it by running some wire.
Dry weight means nothing. Travel trailers are notorious for understating dry weight. If the trailer is under the tow rating (3500 for an SR with the detuned engine), and you are not exceeding the payload capacity, you are good to go.