All of the benefits (so far as I can tell) were always theoretical. We can make our own trade deals. Except, previously trade deals were made on our behalf as part of a trading bloc that included us, Germany, France, Italy, The nordics (mostly via the EEA) and the rest of Europe. How was there ever a serious expectation we'd get a better deal as a fraction of that bargaining power? So, a theoretical benefit that's extremely unlikely to pan out to our advantage.
Taking control of our borders? How has that worked out for us? Not too well so far it seems.
Yeah, it's crap. But I feel like some more of those brexit supporting business owners need to eat some more humble pie before we ever try to go back.