Even if players see they have the freedom to set their own gear [in terms of stats and effects], they will try to find the most efficient combination, so the best-in-slot will be set by someone and others will just follow them. In order to give people interesting and fun content, we made the gear system as simple as possible.
Players aren't stupid. Those who want to try a new build will try, other will follow a guide, and amongst those who follow a guide, they may modify it a little and find something new.
Also, he says the current "system" allows for players to easily get back into the game after a break, and then says that, with customisation, players may blindly follow a guide. Make the link between the 2 statements : players' guides precisely allows other players to easily get back in the game.

Finally, the goal, the motivation of making a RPG in the first place is customisation. In FFXIV, the RPG aesthetic (numbers to increase, gauges to fill, etc.) only serves to build massive walls of chore, and then makes the players feel good with "quality of life" updates that makes the chores a little easier to deal with (and, in worst case, it gives the devs an excuse to sell the jump potion, a.k.a "You can pay us, the devs, to skip the boring part of the game we have built"

PS : On the interview itself, I really appreciate that they have added a summary before the interview.