The main things that cause brakes to feel week or squishy are friction and flex.The things that can flex are the brake levers, the cable housing (shifting under brake cable tension) and the brake arms themselves. Friction can come from all sorts of places.

One of the IAx friction problems is the cable routing through the stem into the frame. There is a cosmetic cover plate on the stem that hides the brake cable housing as it makes an almost 90° turn into the frame. If this is tightened too much, it will crush the cable housing and cause a crap-ton of friction.

I replaced my brake cables with Shimano's BC-9000 Dura Ace cables. They are very good, and minimize a great deal of friction and flex losses.

I do not like noodles, because they add friction. In the case of the rear brake it was an extra-bad choice because the noodle loops out in the path of the cranks. there are a lot of great brake options in the world that are both economical and do not require a noodle.

The other thing you can do to enhance braking performance is improve mechanical advantage. So, I replace my brake levers with TT-78 brake levers. And, I replaced the brakes with Omega X that have a greater mechanical advantage than the simple Tektro geometry.

All of this is overkill, but bad rear braking contributed to an avoidable wipeout on my bike. After that, I dumped the rear brake and replaced the cables and levers. They feel freaking awesome now. They have way more stopping power than before.

Eventually I plan to replace the bars with something that has better cable management. I am working a man-crush on the Alpha X because of the integrated bar and stem, so that will probably be the one.

The great thing about this setup is that now I can have the pads spaced a little further out to allow for fit of 25mm tires. The levers and Omega X brakes engage so quickly (better mechanical advantage) that I do not notice the spacing. I do not need an in-line quick release with this totally awesome brake package.