You'd think if they were using the old code base they'd have more of the old features.

It might not use literal code (although it might), but there's definitely signs that some things like the terrain system were cribbed from KSP1, complete with the limitations of that system.

Which means they've ended up in an awful state where even if they were competant (which they are not), best case things might not be much better.

You're right they marketed it as a full re-write to avoid the problems ("Slay the Kraken"), but what was delivered was trash.