Throat erosion is a combination of mass of powder, type of powder grain, rate of combustion, and velocity of the powder through the throat, not necessarily in that order. I would consider that the mass of powder and velocity in the throat are the driving factors.
.223 barrels seem to last a while. Mine was still around 1/2MOA when I took it off the rifle. That was as good as I could ever shoot it at my skill level at the time. It had over 4500 rounds through it, almost all near max loads with 77gn bullets. Why do they last longer? Probably the small (relatively) powder charge and moderate velocity (for a .22 bullet). If I was shooting 40gn bullets in the 3700fps range it might have worn faster.
.243 is a bit big for the bore. That means it takes a bit more powder for the same velocity as a bit smaller case. That extra powder means more erosion.
As mention\ed above, shooting in a 'hot' barrel will also aggravate the problem.
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