To be honest that's kinda what happens when you have registered further expansions before you actually access them. You gain the benefit of increased level cap but the multitude of quests in the filler patches cause you to level up much to quickly. Sure SE could limit the levels so that you cannot pass 50 if you are still on ARR content, but players with the expacs have paid for the benefit to keep getting levels, not to mention you have access to many different classes/jobs you could get the exp for on the side. Ok no one should be expected to have to level several jobs at the same time just to deal with this (especially if players only like one or two jobs) but the freedom is there and greatly encouraged.

When i came back to the game after some years and created a new character, I just went through ARR on its on and didn't install HW until I was actually about to reach it in order to avoid such a leveling issue but I suppose it can vary for everyone but new players definitely will be catching up with a lot of content and regularly will feel over leveled.