Is it fair for increased promotion in some AFSCs?

I think it is not only fair but it is necessary. There is so much to this answer that is way to in depth to get into but the basics of it is this...we have to have a certain number of each rank in each AFSC. So you kind of have two routes you can take...promote the same % across the AFSCs and then cross-train members to balance the ranks needed, or you can promote more individuals within an AFS to a particular rank and avoid the cross-training. Go back a few years and we went through option A. Maybe you noticed that as soon as promotions were announced, most of those newly promoted received a cross-train notification. In the 3E world we had a need for 3E5 and 3E6 so we promoted 3E2s (which there were no need for) and then cross-trained them to 3E5/6. Then the next year we went with option B. For 3E2 the rate promoted to MSgt was around 12% and for 3E5 it was around 40%. In both situations we ended up with the target end strength for that AFS and grade. I would argue that option B is better because at least you are promoting people that are familiar with the AFS, as opposed to cross-training someone at the TSgt/MSgt level creating a steep learning curve.

There simply are AFSCs that have lower retention for a myriad of reasons. High tempo, marketability in the private sector and so on. As long as we have AFSCs that are unable to meet their targeted retention goals, we will have to promote more in that AFS to fill those vacancies. If you happen to be in a high retention AFS, it means you love your job a little more but you will have to wait to promote (possibly) longer.

Unfortunately the only way to make it "fair" would be to forcibly retrain people based off of their promotions; which would not work. Promotion cut offs, by AFSC, are largely based off of projected rank openings. For example First Sergeants saw a huge increase in promotion to SMSgt because Security Forces called back all of their SMSgts from Shirt duties, which left a need for more SMSgt First Sergeants.

I don't believe 2 years TIG is enough time for development and growth regardless on how high speed you are and that goes for NCO's or Officers. Promoting to fill voids and not based off of performance, experience, maturity and potential will hurt the overall strength of any Armed service in the long run.