I do a lot of fates solo (currently all the Stormblood ones). I have no issue about it. The only fates I skip when soloing are the 30 minutes ones with big boss, else everything is good to solo, at least with my faithful chocobo
However one thing annoying is the upscaled fates. There is no indicator on the map that a fate is upscaled, and the only way to know is to go check.
If it's a simple monsters fate, it's easy to guess by looking at the number of fate monsters presents.
If it's a boss fate, the only way to know is to start damaging it to see how fast you can lower its HP.
And in both cases you still need to move near the fate to check.
So I wish that fates would have an upscale indicator, something like a number (x) at the end of the fate name. So as to not waste my time to go for a Fate that will be too difficult to complete because of the upscale (and that still reward the same amount of Exp regardless of the upscale).