Remember that the core of the sequential turbo system only uses the following solenoids:

Turbo control vacuum
Turbo control pressure
Charge control
Charge relief

Plus the vacuum and pressure chambers as well as the two check valves. Then there are two factory electronic boost controllers which are not "necessary' strictly speaking:

wastegate solenoid
precontrol solenoid

when you do a simplified sequential (or non sequential), you can at least eliminate:

switching solenoid
relief solenoid
fuel pressure/hot start solenoid
evaporative purge solenoid
double throttle control solenoid
air control valve
smog pump
charcoal canister
PCV valve if equipped
split air pipe
EGR solenoid, switch, pipe, etc

provided that you are not concerned about passing visual and tailpipe emissions tests. And if you are hardcore about simplification you can remove the ISC valve and thermowax which will impact idle. OMP removal also reduces plumbing. Both sequential and non sequential don't have to be anywhere near as complicated. You can still clean things up a lot if you choose to remain sequential.

As for Mazda's engineers: I don't have any problems with the way the system was designed overall. If the components were built better there wouldn't be many problems. But they weren't beefed up--they look just like the check valves and solenoids in the 1st and 2nd gen non turbo cars which were not subjected to the same amount of heat.

 

^this is my car also