First of all, no, it's not a common practice to train on bad candidates specifically. I have never heard of this and it doesn't make sense to me. Given how many candidates with solid resumes do not pass interviews, there's no need to waste time on obvious no-fits for training purposes. Many companies don't do any any sort of interview training. Those that do, in my experience, train via multiple rounds of shadowing.
Regarding feedback, almost no companies provide it. Perhaps the recruiter was new, perhaps the hiring team thought you won't take feedback well, perhaps something else. I don't think jumping to "willing to lie to my face" is the right way to think about it. Also, just because the interviewers were pleasant doesn't mean you were doing well. Perhaps there was a lot more to the problem and you weren't going to solve it all on time - again, hard to say, but you certainly can't judge by the interviewer's demeanor. When I was hiring, I wanted all the candidates to have a positive experience, even when they did not do well.
Finally, I'll be honest - you do not come off very well based on this message. It is extremely adversarial, makes a ton of assumptions, and has unrealistic expectations. This approach in fact is a lot less likely to result in feedback, because the company likely picked up on it and is not interested in debating the results with you. The decision has been made, I would suggest taking a breath and moving on. Acing the technical part is absolutely not a guarantee of hire. I have passed on brilliant candidates when the team gave multiple indicators that the person would be difficult to work with.
To be clear, I'm making assumptions here as well and it could very well be that something else is going on. But it would serve you well to introspect a bit and approach the process in a more positive, or at least detached, manner, without making it personal.