SR3 basic priority character creation had one flaw; mundane dwarves and orks who took metatype at D, and magic at E, essentially got their metatype for "free". By letting a human take E for metatype and magic, it re-balanced it.
The main difference between SR3 and SR5 priority character creation is that in SR5, metatypes come with special attribute points attached. So if that same mundane human takes E for metatype and magic, he will have an Edge of 3, while the mundane human who takes D for metatype and E for magic will have an Edge of 5.
I still agree that it can make more powerful characters. The difference between D and E is typically a lot less than the difference between A and B. So I would typically expect to see lots of characters with two priority A's, one priority C, and two priority E's.
I prefer a sum to 20 system with A=10, B=6, C=3, D=1, and of course E=0. It better reflects the karma equivalency (average) between tiers.
I like that at first glance.
I don't feel the concept of "Sum to 10" is broken. Especially not in SR3 v/s SR1 where they lowered Meta Priorities.
But I can see an issue because the priority system levels are not tiered equally which does make for a problem.
I came up with different tiers that altered them a bit based on karma so that the "jumps" between tiers were more equal specifically so that the jumps from E to D to C were on the same level as C to B to A which is really the only problem I have wth Priority.
For example:
One of the things I did was change the Attr levels from 12-14-16-20-24 to be 12-16-20-24-28 (Equal boost at each level)
Most the metas got more SP except Trolls who got less. Humans got quite a few more but started at 1 instead of 2, yet still capped at 7.
Got rid of Group Skills at Chargen and as a whole had much higher skill levels. You can still make a "group" but were not forced into one. IIRC it was something like 40-50-60-70-80 for equal amounts at each level of change.