I was looking for a more general discussion-esque thread on the first page, but sadly I haven't found it so I'll create a new thread.
I'm a Mage in a 10m group currently at 10/13H. We received some terrible news today, aka. we lost our Warlock. While we'd like to recruit one elsewhere, it's not as easy to do so as our 10man team will most likely 'merge' with the other raiding team (at 13/13H) that went 10man during summer recess but now sees a chance to revert back to 25.
Anyway, that's the situation. So not only is our 10man 1 (valuable) Warlock down, the 25m team will need 2 additional Warlocks, while having plenty of Mages. I have entertained the thought of rerolling to something more interesting than my Mage, which I still enjoy, and Warlock has been an obvious choice, while still being relatively similar to the style that I like to play.
One thing that bothers me is the Legendary progression. While my Mage doesn't even have the meta (wonderful RNG, been on it for weeks), I have no idea how crucial it is for Warlocks. If I reroll I want to be ready to contribute on a 13/13H level in 1 month. TLDR: How feasible is it for a Mage to reroll to a Warlock and be ready to help on Animus/Lei Shen 10H progress in less than 1 month time?
Thanks for your expertise . More ideal might be to get ready for SoO, which is a non issue.
For 2/3 specs, the metagem is almost a must. This becomes especially emphasized when those 2/3 specs are operating at almost identical efficiency, whereas the 3rd (that don't need meta) lags behind in output and QoL.
I went from Mage to warlock myself earlier in this expansion, and you'll find the transition to be very easy. Especially concidering that you'll most likely start with Destruction, there will be very small changes in playstyle compared to if you went directly to Demonology.
TL;DR: It'll (arguably!) be doable, but it won't be feasible for 10/13 + heroic progression. You'll get carried - heavily.