To muddy the waters some more, there is whats called a "Stated value" policy. You tell the company what you want for a stated value and they insure it for UP TO that amount, but the contract itself says that they will pay ACV UP TO that stated value, so it is of no real benefit to "state" the value.
That is actually the kind of insurance I carry on my Triumphs, and it suits me. I tell the insurance company the truth (I drive the car to work every day, when it is running and the weather is clear) and in return they treat me fairly when I have a loss.
The first time, the car was clearly totaled (bodyshop estimate was 1.5 times the stated value, and that didn't include fixing the frame). They pulled a set of "comps", meaning a list of similar cars that had sold recently (past year or two) and took the average of that. I had a chance to contest that (by supplying my own examples) but the amount was fair (IMO) and there was no point since it was over the stated value. So I got a check for the full SV, and kept the wrecked car for salvage. I didn't hear what they recovered from the other company, but I assume it was close to everything.
The second time, the car was worth repairing. Neither of us could find a body shop willing to give an estimate, so they made an offer (based on their appraisal) and I made a counteroffer based on the flat rate manual and current prices for new panels. My counteroffer was within about 4% of the SV, and after a few weeks to consider it, they sent me a check. I later heard that they recovered 98% from the other company (which I assume was inflated for my insurance company's costs, including towing, storage and appraisal).
The term "Actual Cash Value" normally includes an allowance for depreciation amortized across the useful lifetime of a product. Since our cars are far beyond their normal "useful lifetime", ACV doesn't really apply to them. So we need to operate on fair market value instead. But, FMV is much harder to determine, especially for a restored car. Hence, the agreed value is arguably the fair market value. Of course, they won't pay that willingly, but there is a good legal argument that it is the actual value. You're right "make you whole" is a vague term and the law doesn't say that specifically. But it is still the legal principle involved. If your car was a 100 point concours winning restoration, one owner with original black plates; then they need to pay you enough to buy another car like it. Not easy to do, and not particularly related to what a "driver" or "10 footer" will sell for.
But, I'm pretty sure the process of subrogation means that they (the other insurance company) get to pay your insurance company's actual losses due to their insured's negligence. That includes legal costs and so on, plus whatever they paid to you.
https://www.irmi.com/online/insurance-glossary/terms/s/subrogation.aspx