To address the OP,
I believe you are right that he had some obvious strengths coming out of college:
incredible/elite RAS
Excellent size
D1 experience (VT)
But.... guys typically become UDFA for a reason. There must have been "some" things that other teams and coaches saw as weaknesses or "lack of polish" to see him as more of a developmental prospect.
I mean look at Allen Lazard as a great example. Some days he looks every bit a true number 2 WR, but he's still not fully developed. He's a great kid and does all the "dirty work" as everyone says (blocking, tough catches, etc) but no one will ever confuse his ceiling with say a Justin Jefferson, Jamarr Chase, etc.
So there is a REASON that some of these guys go UDFA
I feel that with Yosh, it's also a little bit of (and not to take away anything from him) a FANTASTIC OL coaching staff and learning behind Bahktiari and Elgtin Jenkins.
The Packers have long had a great OL coaching staff to develop players, the Corey Linsleys, JC Tretter, TJ Lang, Josh Sitton, Bahktiari (who was a 4th rounder btw), etc. So i think the Packrs OL coaching staff deserves a LOT of credit.
Learning behind Elgtin Jenkins and Bahktiari, combined with his raw tools likely helped him develop in the perfect environment for him to succeed. That's my take.