I'm going to TLDR what I have been saying for a good while now.
Going to Polaris we saw about 10% increase in perf clock for clock, pretty moderate.
Going from Fiji to Vega we can at least expect 20% gain clock for clock, anything other than that is pretty obviously due to driver related problems.
Right now the drivers aren't really working fully for workloads you'd see on a typical gaming card, lots of the more advanced features are disabled.
On the FE card it's mostly meant for tasks other than gaming, and with the very demanding reliability and stability those task demands it's not really surprising that we're not seeing the more consumer optimized drivers yet.
I'm amused by all the headless chickens running around though, Vega being similar if not slightly worse than Fiji clock for clock should speak volumes about the current state of their drivers, and even more so when considering when taking the strange minimum/low frame percentages into account.