I'm pretty sure maturity plays a role. You definitely want your trees as healthy as possible along the way and fungi and beneficial bacteria will certainly help.

Are there any scientific studies making this claim or just some guy in a video on you tube? There are a lot of universities that do a lot of studies and this may have been covered.

Well it's definitely not just some guy saying it, it is proven that mycorrhizal fungi is necessary for figs in the natural world to take up nutrients.  Without the proper nutrients you will not have healthy fruit, sometimes that will mean lower sugar content which will equal bland fruit.

Maturity obviously matters, I mean that is a given in the world we live in.  However part of the reason maturity matters in this aspect is because of the development of the grapevines root system which includes the mycorrhizae.  Mycorrhizae ""roots" are much finer than the normal plant roots and can penetrate down deep into the hardest of clay soils.  They aid in the uptake of 95% of all plants in the world we live in.  Therefore if there is a link we should learn to feed the existing fungi in our soils, this could perhaps in theory give us healthier, tastier fruits sooner.  :)

Actually I said "in theory" in the above but the reality is that this is a fact.

Healthier, yes, Tastier no. I hate to sound argumentative but lets not spread false information unless you have some evidence to back it up.
It's definitely a benefit to add the mico to your soil. You will get a faster growing root system and probably a faster growing plant and may even get higher yields. So i think we are in agreement on most points. However better tasting fruit is not one of the benefits. At least not in the studies I have read. Unfortunately the studies were all focused on tomatoes which root, grow and fruit in one season. Both studies I saw did not notice in a difference in flavor.

I am open to the possibilities but thus far cant find any studies that back up your "Tastier" claim.

When you say no need to add mycorrhizae if there are no microbes one would have to assume that we are talking about using a product.  Mycorrhizae and microbes can be fed directly in the soil as they are already present or very easy to add by simply adding organic matter, compost or forest matter.  According to all research done on the matter plants that have mycorrhizae flourish, take up nutrients more efficiently, and are drought resistant.  The grapevine was designed to work this way, so are 95% of all plants.  

Thanks for the pic!  BTW, hope you enjoy your figs.