I get that argument, but I don't agree with it.
I think you can also make the alternative argument that Burrow had a year for the ages in his very first year in a new system....which speaks equally well of his ability to grow and adapt. He was in Urban Meyer's system at OSU, and I don't think he was as good of a fit for a system that puts a premium on QB's that are able to run. Haskins is the exception there, I guess? Burrow is pretty athletic, but I am not surprised in the least that he didn't play all much behind JT Barrett in that system. He graduated in 3 years from OSU, and transferred to LSU where he saw his first significant playing time in college in a system that frankly sucked. The system he plays in now is great, but I don't think it's fair to discount the fact that he needed to master it in one year and be able to make plays in it (which he has ad nauseam). Outside of the system being good, I see that Burrow throws a very catchable ball, he has the arm strength to make all of the throws, he is extremely accurate with a very quick release, and he processes information on the field at a lightning fast pace. Additionally, it seems that his teammates love him.
When you look at the context of his college career, I personally don't have any concerns about him having one good year. I see a QB that is a leader, works very hard to learn and adapt, is accurate, is on the upper end of athletic for a Pocket QB, has very good mechanics and makes sound decisions when live bullets are flying. Isn't this exactly what you're looking for in a high draft pick QB?