"Garbage in, garbage out" - Is it rude to call others' works as 'garbage' compared to ours?
Yes, it's rude to describe somebody else's work as garbage, and unnecessarily so.  You've already said it much better yourself:


  if we used less valid models we should expect less accurate results


There's no reason to confuse this simple factual statement with a value judgement.  Just because something works poorly doesn't mean it's garbage---it may also simply be earlier and less well engineered.  Would you call a Model T "garbage" just because it gives inferior performance compared to a current car?