>really bad at reliability

Yet, the most reliable services people use every day run on x86. It's not "really bad".

>due to its complexity

I don't see the complexity of the instruction set causing downtime. Compilers abstract 99% of it away.

>due to obtrusive (SMM mode), non-auditable firmware.

I've never seen SMM mode cause down time, nor have I had the non-auditability of the firmware caus me down time. These are low level things that are a part of how the CPU works. When you are working at a high level you can just ignore them for the most part. For reliability you are always going to need to be able to handle bad chips due to manufacturing defects once you are operating at scale.