I agree with the readability point. Also makes it easier to balance a larger range of Titans, since they only need to consider 6 (for now) possibilities vs. the teeming multitude that comes with a loadout system.
Could they have gone another way? Sure, but barring some questionable balancing decisions, I like the results just fine. Looking forward to seeing what new Titans they roll out later down the line.
ed: I will admit that I'm kind of disappointed in the paint options, though. A lot of them are just garish when you slap them on a Titan, and most of the rest are boring.