2008 was vol 49-51, MF started with 56 which was Dec 2009, so already counted for 2010.
And i don´t count Shabondy (2008) to Marineford, at best you can make the argument for Impel Down but not really, due to the intense draw of MF since battles and war and all.
2008
https://myanimelist.net/forum/?topicid=1323417
Top 50 Volumes
*1 1,678,208 ONE PIECE 50
*2 1,646,978 ONE PIECE 51
*3 1,645,128 NANA 19
*4 1,544,000 ONE PIECE 49
2009 (Impel Down, which for me is pre-Marineford, and had around the same sales per volume as now)
https://myanimelist.net/forum/?topicid=1323425
Volume Sales
*1 2,057,528 One Piece vol.53
*2 1,963,696 One Piece vol.54
*3 1,952,551 One Piece vol.52
*4 1,810,410 One Piece vol.55
Comparison to 2021:
One Piece 98 (2,018,042 copies)
One Piece 99 (1,863,574 copies)
One Piece 100 (1,839,886 copies)
In contrast, MF year (2010) had a 500k spike, one year after even more than 1 mil spike compared to pre-MF, which 2012 held.
Volume Sales (https://myanimelist.net/forum/?topicid=1323427)
**1 2,593,580 One Piece vol.59
**2 2,578,730 One Piece vol.57
**3 2,557,356 One Piece vol.58
**4 2,492,183 One Piece vol.60
**5 2,480,124 One Piece vol.56
Volume Sales (2011) https://myanimelist.net/forum/?topicid=1323429
**1 3,382,588 ONE PIECE 61
**2 3,207,568 ONE PIECE 62
**3 3,073,175 ONE PIECE 63
**4 2,652,700 ONE PIECE 64
Volume Sales https://myanimelist.net/forum/?topicid=1323433
**1 3,336,992 ONE PIECE 65
**2 3,320,744 ONE PIECE 66
**3 3,044,901 ONE PIECE 67
**4 2,390,625 ONE PIECE 68
So it´s basically a 33% decline from its peak sales per new volume and a fall back to 2009.