I am not in favor of the time-based-leveling system but one could see it as a "less demanding" version of the typical MMORPG grind. In most MMORPGs, you grind experience or gold to unlock the next character or equipment level. You are forced to spend X hours/days/weeks grinding to get there.
Instead of making you sink time into grinding, they just automate the process. In either case, you are forced to wait X amount of time to get to the next level, but for the time-based system, you can spend that time doing what you like instead of being forced repeat boring grind.
Unfortunately, players don't tend to see it that way. As pointed out by someone in this thread, because it takes away agency, players feel as if they don't have any control or impact on the leveling process. The time-based system could be timed in a way that it matches optimal grinding, but players will probably still feel bad about it.