More convenient and faster than what, exactly? Remember that before WoD, flying speed and utility was more prevalent than ground mounts. It was considered the baseline for the open world at level cap, except in specific, limited areas. It was the norm.
If we're going to start trying to second guess people's true reasons for enjoying flight, then I want to know how many people honestly, truthfully believed that flight was a problem before blizzard made it into one. I guaran-fucking-tee you it wouldn't be the majority. But we'll never know that because it's much easier for people to suck down the sweet SWEET confirmation bias they get from agreeing with Blizzard.
And even if a few of them are able to objectively look at the differences between flying and no-flying and decide they honest-to-god like the ground game more, there's still NO reason for the two to be mutually exclusive other than Blizzard's desire to apply a single, over-simplified formula to their entire open world design.
Uhg....