1. The outer bridle legs are slightly slack but do tighten up as the leading edge spar bends back due to wind pressure.
The bending back gives the kite a better aerodynamic shape. If the kite stayed dead flat, it would fly like a sheet of plywood, losing a lot of performance and handling.
2. Moving the position of the brake line relative to the end cap has quite an effect. At one extreme: no bridle/connected to the end cap, there is a lot of bending force applied to the vertical spars, making a no bridle option limited to very light wind conditions.
You can get an idea by taking a spar at each end and bending it carefully. You'll find that is easier to bend the spar with your hands at each end and it gets more difficult as you bring your hand together. The bridle legs help reduce the stress on the spar, but also affect the amount of turning.
If you shorten the 'down lines' that connect the upper bridle to the bottom, you start to reduce the leverage you have on the bridle, reducing the effect of your controls. At the extreme: having the 'down lines' too short will cause you to lose quad line control and your Rev is basically a dual line.
You could make a new bridle and use pigtails and sliding Prusik knots, like a dual line bridle if you want to experiment with finding your own 'sweet spot', but IMO, the Rev bridle is a very good bridle.
3. The centre bridle point is an important support for the frame, otherwise you'd either need a stiffer and heavier spar or risk it breaking in wind gusts.
4. I have done some experimenting with Rev bridles, but I found that I got more satisfaction and improved my skills more just by flying more and watching better fliers than tinkering with string & knots.
Note: I am by no means an expert, just a guy that like kites and flies them a lot.
I'm sure the real experts will post the definitive answers soon.