There is significant warmup required, which is not good for most programs. Deegen's approach is very promising for interactive use or other situations that require low latency.
There's warmup to get to the best possible performance, which given that Deegen is a copy/patch baseline compiler, will be far above what Deegen can do. If you only care about Deegen level performance then GraalVM will warm up to that point quite quickly. And Deegen's approach cannot easily go beyond that level because it's not a full compiler.
I think the GraalVM/Truffle guys are also working on a copy/patch mode and warmup optimizations too. So the real question is who gets to full generation of both baseline and full top-tier JIT from one codebase quicker.