i mean the store exist since wrath, so what exactly would be reference point, burning crusade?
but i think yes, it was reflected in the game, lets ignore SL (it was cut short for other reasons, not for the lack of funds, but if we got one more patch with reasonable pacing i wouldnt have issues with it), think about BFA, 8.2 was biggest patch ever, 8.3 had a lot of content, we obviously have far more endgame content than in lets say wrath, graphics and other technical aspects got better over years too, for the SAME SUB PRICE (which now includes classic and tbc and soon wrath classic), despite everything getting up in price...
so yes, not all, but definitely some of the shop money went back into the game... and ofc not all, blizzard is a BUSINES, which have to have profit...
you might argue people didnt like BFA (and now SL), and to extent you are ofc correct, but! more money doesnt mean content will be well received, just that there will be content, "quality" (as people see it, so not really quality) is subjective and completely different issue...