If Scrum is too hard for people to adopt, then that's a valid criticism when it comes to its impact on the wider industry. However, what we can't do is fail to adopt it properly and then generalise our criticism of that new process to encompass Scrum as a whole. Its ideal version is not some platonic form that cannot be realised in practice; I have experienced it first hand and it can work reasonably well. I have also experienced all sorts of 'flavors' that were less successful. They usually amount to people either not bothering to RTFM, low levels of investment in process, or senior management undermining the team efforts (through either not RTFMing or not believing in Agile as a concept). Whether that is down to the lack of adherence to the Scrum process itself, or just the lack of competence that would be required to stick to any process is an open question.

Scrum as a set of process rules should not be particularly difficult for an engineering team to learn. I submit that if a team cannot operate under such a set of rules, it will be unable to adopt any set of process rules, and in addition to that, it will perform especially poorly under a system of no rules (i.e. direct rule by edicts from kings and queens).