Many plant species look very similar and behave similar, so I don't think every Russian/Soviet era plane is a direct copy. The BAC111 came before the DC-9, and the Caravelle before the BAC111.

Since the fall of the "wall"/cold war, etc., I've been able to talk with many pilots who flew Russian/Soviet aircraft who had also flown comparable western aircraft. I've also been able to talk to westerners with 50+ years in commercial aviation who have been able to get into Russian aircraft. The general agreement is that the Russians have excellent build quality, efficient wings, and good handling. The shortfalls were (are?) with engine efficiency, power output, longevity and especially with advanced electronic systems. Some time ago I was able to get a hold of some performance numbers of a later variant of the TU-134 and compared them with the DC-9-30. The TU-134 weighed about 30% more, used about 30% more fuel, 30% more runway, and had 30% less range, and probably had a 3rd crew member. That was awhile ago, so I don't know if the ratios are still the same. One exception was a pilot who preferred the TU154 over the B727, but he said he wasn't paying for the fuel.