A car analogy!
Suppose you were shopping and the slick-haired dealer in his very nice Armani suit presents you with two very nice model, priced similarly. The smart buyer you are, you immediately request the dealer to hand you a specification listing both model's feature. Ever discerning, you immediately notice that one car outperform the other car in every category. It has higher top speed, more horsepower, more volume capacity in trunk and passenger space, has six cylinders over other's car four, comes with dual-head carburetor, set of all season tires, and my goodness so many more! It clearly has to be a better value, surely! You get excited, work out a acceptable price with the slick-haired dealer in his very nice Armani suit and as you happily hop in your brand-new (and powerful!) car, it starts up with a growl as if it's ready to go on the prowl. You gingerly drive out of the dealership and into the nice little country lane for a spin. The first thing you encounter is a sharp turn, almost 90 degree. No problem! You start to turn into the curve and ...
WHAM!
You find your nice little new car lovely wrapped around an oak tree. Thinking back, you merely had turned the steering wheel and it oversteered.
As you contemplate the last few seconds, you fill with horrible realizations. Not only you neglected to take it out on a test drive (and thus discover that it had awful handling) but also:
The specifications doesn't matter a damn because it never lists what you actually need out of the product.
Whew, that was quite a windy and circuitous way to make the point that Galaxiom drove home earlier; 7 TB is great on the paper but in practice, I'd bet you would be in a world of hurts. After all, it's the marketing's job to sell the product, and they like nice little numbers even though they represent the absolute limit but almost never the practical limit. By same token, Access's specifications claims to be capable of 255 concurrent users but it's seldom that anybody has a successful Access application capable of supporting 200+ users, let alone just 30 users.**
Next point to consider: Microsoft offers several products, while FileMaker just offers its own products, so in a sense, FileMaker isn't just competing with Access; it is also competing with SQL Server and Sharepoint and just about any other products that performs some degree of data storage & searching/filtering/reporting. On the other hand, Microsoft has to ensure that it doesn't put itself in unfortunate position of having Access competing with SQL Server or vice versa so it has to put down some kind of boundary. As pointed out, it's fairly seamless to upgrade/upsize/scale when the needs arise, and you're not even limited to SQL Server! Prefer Oracle, DB/2 or PostgreSQL? Sure, you can use them with Access if you want.
I do have one more advice: Go to FileMaker forum and talk to people there. See what they have to say.
**I've heard of reports of Access successfully supporting 100+ users, but I don't know whether it was a pure Access solution (which would be impressive) or using ODBC backend (which is very possible).