Correlation does not imply causation. The reason we have fewer players now has very little to do with preferring the older style of gameplay. There are many, many factors at work.
You're right the numbers don't lie. The problem is your interpretation of those numbers is flawed at best.
The most obvious factor is simply the game is old. People move on. The fact that there are fewer players now than many years ago does not imply the game is now bad when it was good before (Even WoW is far off its peak population- Although it remains strong today because of solid marketing). People have myriad reasons for leaving.
Some people left because they didn't like game changes. I know some people who left because they didn't make game changes fast enough (if they don't fix this job soon, I quit; a friend once said to me).
Some people left simply because they got bored of the same old game, even in spite of new content and features, whether they were good or not.
Some people left because new games came out that captured their interest (and that doesn't mean the game got worse for them, just something piqued their interest and they ran with it).
Some people left because they just don't have time for the game anymore. People's lives change, they get jobs, interests change, etc.
Your logic is flawed, because it operates under the presumption that "the old game is better" is the only reason players may have left. For some people, that may be a reason. Ask anyone on the street today if they've played an MMO. If they answer yes, ask them if they've played FFXI or heard of it. Few people will answer yes, and if they've heard of it, its very probable they've heard of it because of FFXI characters in other games (Dissidia FF, Thetarythm FF)
Honestly, FFXI always had a relatively low new player retention rate, because the game is pretty brutal, even to a new player, and even today it still is, compared to other games on the market. They get frustrated and leave before they discover the good stuff. I introduced many players ot this game, even in its early days. Most did not make it past level 10 and most never got to see the epic storylines in this game. So FFXI's real problem to me has always been that it was hard for them to hang on to new players long enough for them to get them hooked.