a couple of suggestions, hope it helps a bit:
- the tone in your email was pretty strong, or, can be taken as rude. because it's not our first language, it happens. you may send a thank you note to your friend, who tried to help
- while your point may make sense, when getting your receipient annoyed, it's not a surpriuse he gets defensive ( especially when copied manager).
- suggest you to reach out to him, to propose a short (15 min. )face to face conversation, or at least a con-call, to explain what is your thought, why you thought so, to at least give him an opporunity to communciate with you.
- in case it works out, great. In case not, then there's a need to talk to your manager to help you to solve the issue.
