Following up on the list I made last post these are the sources of top tier gear in WoW as from the completed roll-out of changes that are coming over the next few weeks.
Weekly Mythic+ cache, up to 410 after a couple of weeks for +10 Mythic.
Elite crafted: bop self-crafted: 415
Possibly BoE world drops (if they even exist will probably be super rare and insanely expensive).
Rated pvp rewards are based on your pvp rank, rank 2400+ for the best rewards.
End of match rewards: occasional 370-405
Weekly cache rewards 385-415
Weekly chest rewards 385-415
World pvp quests (Alliance get a quest to kill 25 horde players awarding a 370 item)
Titan Residuum vendor:
vendor: up to 415 best in slot
Seals of Wartorn Fate
reroll a loot drop
Maximising these rewards for minimum effort gives us:
Raid - progress as far as your guild can go.
Dungeons. Clear one Mythic +10 per week.
Professions: if you're a tailor, leatherworker or blacksmith upgrade your item as far as it will go.
PvP: you want to work on your rating. ilvl this high only comes if you're in the top three tiers of pvp (Rival 1800, Duelist 2100 or Gladiator 2400). Rival looks pretty obtainable and will give a 405 item in the weekly cache.
TR: this is effectively grindable high end epics. You just do the content that offers other lower level epics and melt everything down, slowly inching your way towards the high price of the 415 gear or the even higher price of the specific slot 415 gear.
So there are three progression routes which are fixed. You can't make your guild raid more than it does, there's no point doing more than one +10 dungeon for this level gear (except for melting stuff down for TR) and you only make your profession 415 once.
PvP you can keep plugging away and inching your rating up and becoming better as a team.
TR you can grind by doing all the 370+ epics and melting them down allowing you to slowly inch towards your 415s by doing warfronts, emissaries etc. This is probably low priority filler activity.
In conclusion most ambitious raiders are going to be doing a lot of rated pvp if they want to gear quickly.