To be very clear, redlining didn't happen just because a bunch of individual bankers happened to be racist. It was a consequence of federal policy -- the FHA would insure loans in white neighborhoods but not in minority neighborhoods, so even for a rational banker uninterested in race, it made sense to issue the loans for white home buyers, and not minority home buyers, even if they were financially qualified. The "redline" choices were not where a bunch of separate banks had independently decided that some "bad risk" threshold was crossed -- they were picked by HOLC/FHA. The FHA also subsidized construction of white housing developments, but not minority ones.

When people refer to "systemic racism", the "systemic" part is typically literal.

Also, I invite you to take a step back and interrogate the examine the implicit premises of your question. I think you're saying that _in a free market of rational agents_, it doesn't make economic sense to not issue loans to people who _aren't_ credit risks, and I would agree -- except housing segregation was always about a heavily artificially manipulated (not free) market, in which people of color couldn't purchase a home in a white neighborhood regardless of their willingness to pay. Public policy bent over backwards to coerce all parties to maintain segregation (e.g. sundown towns, racial covenants, etc), ironically including during cold-war years when the US simultaneously tried to be a global advocate for free markets.