Comparison data for the mans:
Pokemon MD1 (DS) had 134k week one, GBA had 121k week one (total 255k week one).
Pokemon MD2 opened to 583k week one.
(Both finished at ~1.5 million)
Pokemon RuSa opened to 1.25 million week one, Emerald to 643k week one (~1/2th)
Pokemon DP opened to 1.5 million week one, Platinum to 967k week one (~2/3rds).
So what we can see is that PMD did not grow from 1 to 2, that it became substantially more frontloaded, that PMD2.5 is smaller compared to PMD2 than either of the recent Pokemon.5 games is compared to their mainline games.
all in all meh