Without paying 55 quid for the book I can't tell if you are drawing valid conclusions from the research.
It seems, frankly, quite bonkers to assert that 'most letters are never looked at at any stage'; why are they there in the first place? How do you 'know' which ones not to look at? What information tells you what each word 'says' (no, don't tell me, most of the words are never looked at, either..)
Of course it makes sense; this is why those "read this even though all the vowels have been deleted" tricks work,
No it isn't. Those 'tricks' work because a skilled reader is able, to a certain extent, to deduce what the words might be. However, if I were to delete all the vowels from this message I would be extremely surprised if you could tell me, completely accurately, exactly what I have written. And, if you weren't a skilled reader you wouldn't have a cat in hell's chance..
Try this:
thnk tht ny npd wrk s mmrl -whthr, s Hrrs pts t, t s Jcst nd Crspns mkng th t t cty lw frms r pnrs wks ftn spnt t th bttm f th srvc sctr. Th Crspns nd Jcsts my b n pstn t wrk fr nthng n th hp f jb ffr t sm nspcfd tm n th ftr bt tht ds nt mn tht thy shld. trnshps dstrt th lbr mrkt:thy r ftn nt dvrtsd s r nly vlble t ths n th knw nd r jst s mch xplttns xpctng jbskrs llwnc clmnts t wrk fr fr. Th bn f m lf s nvrsty crrs dvsr ws ths stdnts wh, bcs thy cld wrk fr nthng wr lkly t b shhrnd nt th pck f th grdt pprtnts, s cmprd t ths frcd t flp brgrs r pll pnts t rn mny.
The original, with vowels, takes me 22 secs to read.