It's not really a massive change, there are 10/15 jobs that start at lebel 1 already.
And sure, I get that you like to play a class with as much of a full kit as possible. But the trouble with it is that while you enjoy having that kit, any time you find yourself synced below the start level, people complain that the class doesn't play well at lower levels, or that it's missing things. My opinion is that this is because when you start out at, let's say 50, you learn to play the job at 50 and above. You don't learn how to play at lower levels because you're used to having all this kit.
Sure, maybe you'll learn bad habits that later on you have to unlearn, but I don't consider that a bad thing because you understand WHY you're not doing that any more.
Some people like having at least most of their kit, I understand that. But there's no reason you can't level from 1-50 to achieve that, and then never run anything lower again on that job. Suppose you wanted to be a warrior, but only from level 50. You only have to get those 50 levels once, then you're in exactly the same position as if you picked up, say, red mage.

To steal a line from you (because turnabout is fair play),
There's really no need to force such a massive change on everyone else because people can't find workarounds the existing system.

Your workaround is the first 50 levels.