It will be up to date but not "Optimized" for mythic raiding. You may be top dps in LFR or even heroic, but in mythic, specially if you're in a good guild, you get yourself into a competition. So you need to be at your best if you want that fixed spot in the roster.
About classes, right now overall in mythic raiding, ww is doing a better job but it varies from fight to fight. For example you see only ww monks in top dps chart on twin ogron fight, but for example in Butcher mages are top. Melee sometimes is a little harder to manage, cause we are always under bosses balls! And always in danger of any spell coming from boss, as a ranged dps sometimes you have enough time to run away or dodge a spell. But srsly just go with any class you really like. I went with Monk cause I like the playstyle and I also like to be a healer as os. If you only care about dps outcome then you have to change your class every fcking patch, cause this patch monk is top, next patch they screw it with the nerf hammer (just for instance! I'm not exactly talking about next patch per se) and you're at the bottom, who knows what happens after that.
For arenas and bgs it's totally different.
