Would a really old fig tree have a better quality fruit because of
the root depth and the thickness of the bark?

In the long run speaking, would a fig tree trained as a tree bear better fruit or a bush?

Would an in ground planted tree would bear tastier figs or potted?

Does size matters?

Excellent question , i will like to know that as well

As far as potted figs vs. in ground figs, I still say it has more to do with soil conditions, climate, rain fall, humidity, and such...I have tasted figs from both, and the bottom line is that a good fig is a good fig, whether or not it's in ground or in the pot.
As far as the more mature tree vs. the younger tree, I can only give an example: the first two years our tree produced no fruit...3rd. and 4th. year it started to produce fruit that had a pretty good taste...5th. and 6th. year it produced 300 to 350 figs and the taste had definately improved...this will be the 7th. season, and I'm believing for even more figs and better tasting figs....."fingers crossed"    :) 

Lena...I agree with your point about a 50yr. old and 20' tall tree...I think there is a certain age of maturity when the figs produced by a certain tree are at their optimum taste level, maybe 5 to 10 yrs old...and at that point they level off...although there is no reason why the 50 yr. old tree cannot maintain that same great taste.