You've gone from a top 0.1% athlete to an average Joe. Nothing stopping you from getting back to where you were except time. Accept that a lot of work needs to be done. This season is a rebuilding season. Next season you will be close to where you were before. 2019, if you keep it up, you should be back in full.

When I was 24 yo and in elite conditioned road racer, I had a very serious head injury. I got back on the bike much sooner than you to race one last season. (11/3 my accident. Back on rollers in February, the road in March. September when I rode my last race, I was still a shadow of the racer I had been.

Unless you have pressing goals that cannot wait, watch carefully that you don't overdo it. I came back too fast, broke a few "rules" re: knees and have paid for it with a life-long condition. (That last season I knew before going in was it; that I would never pin on a number again. So I rode and trained to be the best I could possibly be that season. No regrets, despite the injury I inflicted on myself.)

Keep your head up and plug away. It's so worth it, even despite the time and challenges you will face.

Ben