In my small sample size (3 JL RTW, City II, Lopez, Woodcote, 1 EG, Oakdale), JL uppers wears more supple and form fitting and soles wears more flexible. EG wears more stiff at both suppers and soles. Haven't lived long enough to know the difference after 15-20 years of wear.
According to my research on construction (online and print), both are GY welted (poor construction) but use leather foot beds/insole and rest of the components are top notch. The insoles seems to be decent quality but still far from hand sewn welted insoles. EG has slightly broader gemming. EG uses leather shanks and JL uses steel shanks. BUT aside from the inferior GY welted construction, JL uses heat formed plastic for toe and heel stiffeners while EG uses heat formed plastic stiffeners at toe only. Real handmade shoes uses leather stiffener.
Why exactly would you call the GY welt a poor construction method?