[thxbb12]

Yes, FF could be a compact system if a manufacturer wanted it to be. With equivalent lenses a FF system could be made about the same size as an APS-C system.

Here are a few examples comparing Fuji X vs Sony FE:

• Fuji 14 f2.8 vs Samyang 18 f2.8 : The Samyang features a wider FL (18mm vs 21) while being about the same size and 1 stop faster (in term of system equivalence)
  
• Fuji 35 f1.4 vs Samyang 45 f1.8 : The Samyang is about the same size but faster (f1.8 vs f2.1 equiv)
  
• Fuji 16 f2.8 vs Samyang 24 f2.8 : The Samyang is smaller while being 1 stop faster (in term of system equiv)
  
• Fuji 16-55 f2.8 vs Sony FE 24-105 f4 : The Sony is 1cm longer and about the same weight as the Fuji while being slightly brighter (f2.7 equiv) and featuring a longer range (105mm vs 83mm).
  

It's just that FF manufacturers aims at producing the best possible optics at the cost of size, weight and price. However, they could offer slightly lower end lenses in a much smaller package as Samyang is doing.

I'm personally more and more interested in Sony FE because it's attracting a lot of 3rd party makers willing to fill this gap. Sony was smart in opening up their mount protocol to others.
I believe it is a big mistake on Nikon, Canon and Fuji's part to not open theirs up.