The offense will be fine. Mac was nails the other night. That was the best I've seen him in terms of footwork, posture, mechanics, pocket movement, and consistent attention to detail in general. He wasn't letting himself throw off his back foot, falling away, and some of the other sloppy habits he had shown at times. I was lowkey thrilled at the performance he put in.
Adding a modern, athletic ILB (or two) who can play in space gets the defense about 75% of the way there. They still need another CB and DL, but a competent ILB gets them a lot of the way there. If Nakobe Dean gets anywhere near them, they should jump all over him; if Jordan Davis or another high quality DL/LB fall along with Nakobe, pull a Jones-Hightower part 2 and grab them both. In terms of solutions on the roster, we can cross our fingers for McGrone and McMillian.
Beyond that I'd like to see a new ST and DL coach. Something that flies under the radar is that DL coach Brendan Daly (who joined the team in 2014) left following the 2018 season to join the Chiefs. Since then I feel like there has been a subtle but consistent drop-off in DL play.