You and Blizzard seem to not understand, that there are different ways to "actually play the game" and enjoy content and that this ways can change with time. I highly recommend you to read
"Designing Virtual Worlds" book - "bible of MMO developers". Big improvement of MMOs in comparison to earlier game genres - is that they cater to widest auditory of players, not some narrow niche. The way, player enjoys content, changes with time. First you enjoy gaming process itself - first games, arcades, were catering to such kind of players. When gaming process stops being interesting for you - you stop playing such a game. Then you start to explore game - first you want to beat this game to see, how it ends, then you start to find some secrets and hidden paths. So games, that had some story and lore were implemented. Then you start to achieve some goals in this game in order to beat other players - something like max score, fastest run, beating game on hardmode, etc. So next improvement in game industry was - implementation of games, that had competition. And the last thing, that can be fun, after all other things have been already done - is playing with friends. Socialization - was last improvement, implemented in game genres. That's how MMOs have been born. And in case of xpack and content patches players can temporary change their interests - cuz there may be new gameplay, new things to explore, new goals to achieve.
Biggest Blizzards' mistake - is that they assume, that when they release new content, players start enjoying gaming process itself, like game is brand new and fresh, for at least a year since it's release. They are wrong. There is no way back. When new content is being released - players usually look for content, they were doing in the past xpack. For example. Yeah, I was doing some random stuff just for fun and was enjoying gaming process itself at release of WotLK - first xpack since Vanilla, I was playing seriously. I was even ZOMFG doing some PVP... Fuuuuuu! But then I discovered 5ppls and raids. And I have been doing them since 3.0 and till release of Cata. And when Cata was released, then guess what? I wasn't doing some random stuff just for fun - I immediately looked for 5ppls and raids to do. And biggest Blizzards' mistake was - to say "Heroics and Raids aren't for you". At the end, after trying to adopt to this situation, it leaded me to quit the game prior to 4.2.
Same here. I have been doing WotLK content with flying. I have been doing Cata content with flying. It was big mistake to assume, that I would enjoy MOP content without flying. And I have been doing Tanaan with flying for months. There is no chance, that I will enjoy no flying again, no matter, how good ground content on Broken Isles will be.
So what? Blizzard assume, that when they will release Broken Isles, players will start enjoying them the same way, they were enjoying game, when they were playing it for the first time - somewhere back in Vanilla/TBC/etc. No! It's just nostalgia! Nothing more! There is no way back! Players will enjoy content this way for a week may be - then they'll want to have flying back, cuz doing the same World quest again, again and again without flying - is pure tediousness and annoyance. And refusing to bring flying back at that moment will cause large amount of damage to game, as it happened in WOD.
I understand, that Blizzard do it, cuz some players tell them, that they miss those old times, when they enjoyed doing some random stuff just for fun. But this is just nostalgia - nothing more. And Blizzard kill their game for players, who still enjoy it. Cuz taking content away from players, who play it to achieve some goals, not just for "temporary" fun, in order to give it to "cyclical" ones = automatically losing half of playerbase. Most stable part of playerbase. And Blizzard risk to lose both stable and cyclical players, if they will continue towards this direction of development. I don't want it to happen, cuz I still enjoy Wow.