...and all of this was good for nothing, really. I fail to see the benefit over simpler motors of the same size from a decade and a half ago that make the same power, and now have a decade and a half of track-record for being reliable...
That is one point of frustration for me. All of this technology didn't do much/anything for me, the end consumer.
This is not just Mazda. All automakers are using all kind of technologies with expensive cost just to improve a couple of MPG's. This certainly may not impress you and many consumers. But they have the CAFE standard and many regulations to meet hence they have no other choices. SkyActiv Technology has helped Mazda to survive otherwise their cars became uncompetitive! Use US version Mazda3 as an example,
2011 Mazda3 2.0L w/5-speed Auto (last model year without SkyActiv)
Horsepower: 148 hp @ 6500 rpm
Torque: 135 lb-ft @ 4500 rpm
Compression Ratio: 10.0:1
EPA MPG: 24 City/33 Highway
Curb Weight: 2922 lbs
2015 Mazda3 SkyActiv 2.0L w/6-speed Auto
Horsepower: 155 hp @ 6000 rpm
Torque: 150 lb-ft @ 4000 rpm
Compression Ratio: 13.0 : 1
EPA MPG: 30 City/41 Highway
Curb Weight: 2917/2918 lbs (Fed/CA)
So you can see how much improvement the SkyActiv has done to Mazda with the minimum cost. To me, that's remarkable!
Fuel efficiency is the consumer-oriented result of the technology. I recorded 25-31 mpg in 30K miles from a CX-5 GT 2.0L being a 3400 pound AWD SUV equipped with latest lux and safety features and that mileage is way better than anything available a decade ago.
I averaged around 25mpg around town and 30 on road trips in my 3100# FWD 2002 Infiniti g20 with a 4 speed slush box. It had 145bhp and 136# torque. I'd say that's very comparable given the 4 speed slushbox. Slap that motor in your cx5 and I bet it would be within 1 to 2 mpg.
You should never compare apple to orange as you did here. Comparing a CUV, a Mazda CX-5, to a compact sedan Infiniti G20, is simply unfair! In addition to weight difference (3433 lbs 2016 CX-5 Auto FWD vs. your 2961 lbs 2002 Infiniti G20 Auto), the height and high center of gravity all make differences. Let's compare your old G20 to comparable 2015 SkyActiv Mazda3 above:
2002 Infiniti G20 2.0L w/4-speed Auto
Horsepower: 145 hp @ 6000 rpm
Torque: 136 lb-ft @ 4800 rpm
Compression Ratio: 9.5 : 1
EPA MPG: 23 City/30 Highway
Curb Weight: 2961 lbs
Now you can see bigger differences between the two, especially on gas mileage, right?