S- channel isn't the simplest solution, it just the most efficient from signature point of view because it cause the signal to bounce multiple time and accumulate the radar absorbing effect of the RAM layer. Engine face blocker was first used on F-117 ways before S-duct were designed and used on F-22 and F-35. Engine blocker also used on F-18 E/F
YF-23 and F-23EMD both used S-duct, but the one used for RCS evaluation is F-23EMD which has more prominent S-duct and a DSI inlet
Something is built later doesn't automatically mean it is better on all front, X-32 was built 10 years later than YF-22 and YF-23 and it is slower, carry less missile , with smaller radar, less agile .... so on. The point is: they have different requirements.
No one ever said Boeing engineers are stupid, no need to repeat that, it is a strawman argument. S-duct and turbine blocker has their own advantages and disadvantages. Blocker has advantage in lighter weight and smaller volume while S-duct has advantage in signature. You can have two design satisfied the same requirement and yet they can be different. For example: let say your requirement is making a fighter that can fly faster than Mach 1=> F-35 and F-16 can satisfy that but they aren't equally fast.
The whole point of the blocker is to stop radar wave from reaching the turbine blades, if you make them transparent to radar wave then what the point of having them in the first place?
