Let me give you a simple example, the drow.
It's CR+1 and LA+2.
So he starts behing normal CL, but eventually at late game, he would completely get rid of her her LA, while still counting as CR+1, thus pulling ahead in CL to other party members once exponential exp catches up.
Lets make sure I'm understanding what you're saying, the LA buy-off rules, and my own rules. For now, we'll assume LA works exactly as-is (which is, dubious at best, of course
).
ECL 3Everyone in the group has a 3rd level PC. You roll up a level 1 drow wizard. Your CL is 2 because your CR is 2, despite being ECL 3. This is technically a boost to the current system, but not much of one, really.
ECL 8Everyone is level 8. You now have 6 class levels, so you can buy-off one of level of LA for some XP. You're now ECL 7, but still 6th level, still CR 7, and still have a CL of 7. At this point, all of your numbers match up, but you're a level behind the party. You start earning XP faster until you catch up to the rest of the group.
ECL 10Everyone is level 10. You've caught up and you're ECL 10, presumably, and you have 9 class levels, allowing you to buy off the rest of your LA. So you do, you're now level 9, ECL 9, but still CR 10, and thus CL 10. So, at this point, you're casting like the rest of the group, but you're an actual level behind. Again, you start gaining XP faster than everyone else.
Within a few levels, you will be the same level as the group, but your CR will be higher, and you'll be a better caster.
So, did I understand this all right? That being said, I think it highlights the existing problems of the LA system and the buy-off "fix" pretty well, and it exaggerates them both a bit.
Personally, I guess I'd rather just avoid LA all together, and come up with some way to either re-write LA 0 versions of various races, or figure out ways to tweak it with new RHD, or something.
Good catch!