With the recent patch (6.3) the amount of fate granted at higher levels has been hit fairly hard.
I'm level 50 powerlevel 1445 I used to get around 20 to 28 fate for doing missions around my level meaning 4 to 5 runs and you can do a tarot mission.
Since the patch the most I have gotten is 2 admittly I've only really got white and green missions but from chatting to people it seems even red mission at around my level give 3 to 4. Meaning between 45 to 23 missions (50 and 25 for a shaping)
Your looking at a fair few hours none stop grinding to get enough fate for even a single tarot mission now.
This is going to be a aweful grind to high 50 (and potentially higher) as it is.