Actually as long as you have access to the lower level APIs changing that stuff out whilst not trivial isn’t that crazy. The big win with UE in particular is then phenomenal art pipeline and tooling which would take an age to reproduce in a custom engine.
> The big win with UE in particular is then phenomenal art pipeline
This is the only fear I have with 100% DIY - If I want to go much beyond 90s graphics, I will need to do a lot of extra work (aka "draw the rest of the owl") to even begin talking to artists.
That said, there are ways to build games that do not require elaborate art tool chains. AAA visuals are the antithesis of my target. I am perfectly happy trying to do art in code until the wheels pop off the bus and I have to retool for an external art team.
