One has a lot to do with the other. Class first leftists claim class is the biggest oppression because it is 'larger' than identity. My point is that race and ethnicity can be perceived as larger because they are fixed at this point in time, and will be as long as White people insist on ignoring their massive racial privilege, or the demographic shifts. That is, once I make money, I am no longer poor; this indicates to me that poverty can be temporary. However, no matter how wealthy I become, I STILL have to deal with racism: this never goes away.
So, I am stating that it may very well be easier to see racism as central, not economics, since many people climb out of poverty but nobody can escape the social consequences of race regardless of wealth.