They're the best source. The math is meaningless because it's most often wrong and the game isn't transparent. At best it's useful to figure out how to play or which talents are best in what scenarios. Doom Wolves is absolute shit in this patch, for instance, and it was quite strong in previous patches, but nobody's "math" has indicated this is or was going to be the case. Most of these predictions are wildly off of the numbers we actually see by people who reliably hit 99 and 100%s on live, and comparing the logs of these people is by far the only useful measure we have, on beta or live or anywhere else. Simcraft isn't as accurate as looking at statistics in logs:
http://www.simulationcraft.org/reports/Raid_T18M.html
vs
https://www.warcraftlogs.com/statistics/8#dataset=99
Yep, beating people with 99-100% ranks on live and in world top 10 guilds in mythic+s on beta means nothing. Do you even manage to get blue ranks on live?
Uh, no. That's completely false. On beta tanks do tons of DPS as do resto druids. Good DPS classes do more, but ones that get nerfed over and over well below the bar for what is competitive don't. On live most tanks beat SV and PP beats most DPS.
https://www.warcraftlogs.com/ranking...&spec=Survival
vs
https://www.warcraftlogs.com/ranking...pec=Brewmaster
https://www.warcraftlogs.com/ranking...pec=Protection
https://www.warcraftlogs.com/ranking...ght&spec=Blood
https://www.warcraftlogs.com/ranking...&spec=Guardian
and hilariously
https://www.warcraftlogs.com/ranking...pec=Protection
https://www.warcraftlogs.com/reports/all/11
https://www.warcraftlogs.com/reports/all/10
https://www.warcraftlogs.com/reports/all/9
I've looked at thousands, probably closer to 10k beta logs at this point, and yes, 99% of you do play Enhance like garbage. Even watching good groups on streams who don't public log they're still behind.