Your technician/mechanic probably knows to do this but the master cylinder should be bled (2 bleed screws on the engine side) after the four corners are bled. A brake system flush every 2 years is not a bad idea, imho.
Unfortunately it only made a modest difference. I do notice a slightly better pedal feel but sadly it wasn't what I was looking for. When I had my 2 piston Cobra brake kit, the pedal firmness was much better. My SSBC 4 piston kit had an excellent pedal feel when I first got them but 3 years later... the pedal feels mushy.
A "mushy" pedal can generally be brought on by three things:
something compressible in the lines (like air)
internal or external leakage
mechanical deformation in response to hydraulic forces
You've bled the lines and hopefully have gotten all of the air out of the system ruling out point 1.
An external leak would be obvious and evidence by brake fluid on the ground. Assuming you don't see any you can rule out that. Internal leaks are trickier because they don't leave any evidence with the exception of reduced braking feel and performance. A leak occurs across the seals of the master cylinder, for instance, where fluid from the high pressure side leaks past an O-ring and gets back into the reservoir. This generally results in a pedal that is soft but also one that sinks slowly as pressure is maintained. The cause is often bad seals or corrosion in the bore of the master cylinder. This can happen if water gets into the fluid and it's left there for extended periods (e.g. winter storage months...)
Mechanical deformation occurs when parts give and bend. Pressure that would have gone into pressing a brake pad against a rotor instead goes to deforming something. Modern brake systems are pretty robustly constructed (though it's worth inspecting brackets, sliders, mounts and the like) but one thing that can "give" is brake lines. They can expand when pressure builds, resulting in a mushy brake pedal feel. It may be a sign that a brake line is on the verge of bursting so get it inspected... Other parts can mechanically deform too: The hydroboost and master cylinder mount to the firewall. Make sure it's not deforming or bending in response to pedal pressure.
One other thing that can mimic mechanical deformation is bad wheel bearings. If the rotor is wobbling due to a worn wheel bearing it can push the pads away from the rotors a bit, leading to an initially mushy feel and extended pedal travel when you get on the brakes.