Conditionals - Glossary Definition - UsingEnglish.com
ii) Second Third Mixed Conditionals
If + Past Simple, + Would have + Past Participle
1/ To avoid the illogicality of saying 'If I had been you', which means that I was not you on that occasion, but could be in the future, which is, of course, impossible.
eg:If I were you, I wouldn't have done that.
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I came across this on a page about conditionals.
Does 'if I had been you' have to entail that "I" 'could be you in the future'. I don't think so.
What's illogical about saying, "if I had been you", meaning only at the time of the particular situation. Counterfactuals are often, by their nature, both illogical and impossible. Does changing to "If I were you" make it any less impossible. Again, I don't think so.