You ignore what Blizzard did with gear. They won't change our crit dependency (and some other classes dependency on particular stats). We started xpac with high levels of crit already, we have 50% crit in first tier of content.
Blizzard decided to balance classes differently then in previous expansions: before secondary stats grew at the same rate as int with ilvl. In Legions they won't. There won't be situation of Icecrown CItadel gear which allowed reaching softcaps of stats and stat starvation in Naxx. In legion at the beginning of the expansion high secondary stat ratings on gear were already given as a baseline so that stat dependant spec gameplay didn't change much between major patches. Crit in Argus patch shouldn't be that much higher then now, it's int that will scale much more.
That 'low crit' you're talking about is found only on people who don't do anything beyond Heroic dungeons. Anyone who does Mythic+ and raid has gear to have comfortable levels of crit already. WHen in next patch players will catch up in ilvl, they will have comfortable levels of crit too.
Devs balanced Fire (and some other specs) hyperscaling through stat increase with ilvl on gear.
Look at
tier gloves. 55 ilvls of increase give only 0,28% more crit while Raid finder gloves have 1,22% of crit baseline. So most of secondary stat is included on a base level, stat increase with ilvl is somewhat small. 55 ilvls increase Crit rating by 23% and while int is increased by 67%.