Even without the injury, defenses always figure out mobile QBs including guys like RGIII and Mariotta.
Aaron Rodgers and Favre were different because of their immense arm talent.
And honestly, unless Mahomes becomes that good, defenses will figure him out
Yes and it also has to do with the QB's ability and give-a-F of working to be good in the pocket. Using Goff as an example the moment I knew he'd succeed was when he stood up at the mic the end of his first season and promised he'd do what he had to do to fix things. He immediately signed up with Tom House and his group and worked his butt off from there on to be the guy we see today.
Guys like RG3 meh. He was more concerned with endorsement deals and how wrong the coaches were if things didn't go perfect for him, which of course they didn't when they tried to put more on him. Lots of the athlete types it comes easy to early on, they simply beat defenses with their athleticism in college and in their first year in the league the blitz is cautious due to their ability to threaten the edge. But over time they'll get beat up if they don't transition to playing well from the pocket and benefitting from the protections of the rules.
Mahomes is already good from the pocket. He is clearly a good kid who is interested in mastering his craft, so I think KC found themselves a great QB he just needs to be careful with the running and prioritize his health and living to make the next play.