I see what you're saying from a rhetorical standpoint: it would perhaps be more effective at uniting the democratic base against feckless and corrupt leadership if we drop the lateral-proximal political spectrum dichotomy.
But from a purely descriptive standpoint, there absolutely is a difference between progressives and centrists. 'Centrists' in this context is shorthand for "fiscally conservative neoliberal establishment corporate dems committed to the status quo and appeasement."
Whereas 'progressives' refers to "the party caucus fighting for the working class, reparative justice, pro-social policy, meaningful climate action, and other necessary reforms."
One is beholden to large corporate donors, one only answers to their constituents. In practical terms, there's a huge difference.
If we can communicate that better than simply saying "progressives" and "centrists," I'm all ears for the proposed vocabulary we should use. I'm not attached to the labels, I'm only interested in implementing the necessary changes that centrists actively stand in the way of.
About Progress, Regress, and Status Quo
What it boils down to is we have three options: progression, status quo, or regression. Only one of those is viable for the enduring wellbeing of democracy, the planet, and the common good. That much should be clear.
Regression tries to glorify a bygone past and attempts to return to a fantasy of what was, while ignoring the policies that led to the few parts that were actually better (boomers are nostalgic for FDR's economy, so they demand Nixon's and Reagan's policies which destroyed the comfortable living standards they enjoyed growing up).
Status quo attempts to treat the present moment as static, and it thinks we can ride out the coming storm by resting on whatever imaginary laurels a few people have amassed for themselves by creating, perpetuating, and accelerating the problems in the first place.
Progression is the only option that looks into the future, assesses the paths in front of us and says "We can't go down this or that path because they end in disaster. This other path though gives us a chance." The only option that looks at where we need to go, what the goal is, (i.e. societal and planetary healing followed by collective flourishing), and asks "Okay what policies do we need to implement in order to start down this better path?"
It should be abundantly clear by this point what we need to do, and it's incredibly frustrating that so many people still don't see that. And we're running out of time.