It appears to me that the point of adding the +1 to a skill instead of gaining proficiency to a new skill, which yes numerically is better, is that with a higher level of training you have option of better feats. this provides you with more diversity like Bleys Feuerteufel mentioned above.
I do think that the spread is a little small not sure if widening the margin ever so slightly would help (-4 or-3, 0, +2, +4, +6 or 7). As I have not run things to see how the new system truly feels yet but my initial impression is the same. that "opps the new guy is better at climbing than me despite not knowing any of these techniques that I have spent most of my time studying climbing."
I understand that this is inherent in any system that relies on a random variable (dice) but it seems much more prevalent here with only a gap of 5 possible.
Advantages to this is that anyone should be able to obtain any DC which prevents the characters from having to split the party due to an obstacle that only some people can traverse and due to the new Crit system having a smaller spread means there is less crits/crit fails all the time. So again I think this is something that would be helpful to see in action. Hence the point of this play test.