So, assuming 40k chests and a very rough Mythic drop rate, from glory keys, of 1/6000. The subsequent 1/600 chance for gem chests temporarily turns to 1/1200 until guardians have been ascended.
Every 3 weeks for a mythic?? I didnt realise. The 225 keys available, without spending money, is dissappointing.
yes the magics are lv10 5*
the rest supposedly lv9 and power still workin on, prioritising glory
and i dont feel i suffer in pvp at all
honestly id like to compare some maxed person pvp choices against mine and see what happens with the gold
edit’': i can beat 3trophy enemies just fine
atm 185 wins 3 looses, 7968 pvp points 528 trophies
i dont scout, but lately i go for revenge more often then the gold so its a couple of lwer trophies matches out there
You forgot about the seals the person gets from buying $$$ goodies 
that’s 1650 = 82 keys on top of your number, so the “potential” max would be 367 (unrealistic ofc, unless we get Rhino back here to whip a team of 30 ppl dropping 35$ every week). That’d make 1468 hypothetical keys every month (so each time a new mythic comes out).
Going with 4 weeks between mythics, it’s 300 keys (4*75 from 1500 seals weekly) you can save up. Increased by extras from whatever your guild-mates purchase, and drastically increased if YOU decide to buy the packs (1k seals from 20$ = 50keys extra). I was lucky enough to get the mythic from guild chests (and it happened on the second “50” of the keys I had saved up since 2.1 came out). Not really expecting it to happen again, one smile of rng 
Returning to the title of this thread, since I was the OP :), I did get the latest mythic, as can be clearly seen in my original screenshot. In a top 10 guild, these things can just magically appear.