I was playing a Demon Hunter since prior to Legion's release date, then swapped to a Mage around March and finished leveling her to max level in April, when I made up my mind to change my main character. I haven't played alternative characters outside my main character, besides artifact questlines for certain specializations. With only playing one character and gearing out one specialization, the drop chance of legendary items hasn't been too bad for me (one every two weeks or so). I only need two for my main specialization, then I'll work on my other specializations, which comes down to needing five for each. However, some are luckier than others, but those with split character progression, I see where it's an issue.
Legion is not alternative character friendly. What is one to expect though? If a player is doing all of these outlets for chances on multiple characters (old raids, PvP, emissaries, etc.), legendary items should drop more frequently for them. If someone only logs in to do emissaries on multiple characters and that's all they do, with doing other stuff every so often, should legendary items drop as frequent as someone who puts more time into this game? I don't think so, and that's just my opinion on the matter, but there needs to be better targeting for sure.
No idea if this system will continue on into the next expansion, and I hope it doesn't. As much as I like it... getting a reward of great power and history, I think it's caused more harm than good for the playerbase. Amazing expansion, but this has hinder a lot of individuals, with the artifact grind overhead.