The cost of dismissing what existed before you arrived does not show up immediately. It shows up months later, in the meetings you stop getting invited to think out loud in.
What the research says
Research on organizational socialization describes newcomer adjustment as a joint process, the organization does its part, but the newcomer has to actively seek out and accept the existing culture, norms, and ways of doing things, not simply wait to be accommodated. Newcomers who treat this as optional, who arrive and immediately start proposing what should change before understanding what already works and why, show up in this research as adjusting worse, not faster.
Why the cost is invisible at first
Nobody tells a newcomer directly that dismissing the existing way of doing things cost them anything. What actually happens is a slow withdrawal, less looping in, less benefit of the doubt, a team that quietly stops investing in someone who has made clear they are not investing in what came before them.
Where to start
In your first few months anywhere, spend more time asking why something is done a certain way than proposing that it change. Not because the existing way is always right, plenty of it will not be, but because understanding it first is what earns the standing to actually change it later.
Arriving with the fix before you have earned the context is what gets read as arrogance, even when the fix is correct.
Telling which parts of the existing way are actually worth preserving, versus what is just inertia, is a judgment you will make more accurately once you understand the reasoning behind it. What this gives you is the order to do it in, understand first, propose second.
There is a specific way to ask why something is done a certain way that reads as genuine curiosity rather than as quiet criticism, and it is worth having ready for your first few weeks.