21" Passenger Cars - Reflections

I don't have any so please forgive me if this has been covered elsewhere. When Lionel introduced their new 21" cars several years ago, seems I remember many of you noting major shortcomings in the trucks and couplers. LOts of returns to dealers and the like. As beautiful as they appeared, I got the impression that we had better stick with K-Line or even the 21" Weaver aluminum cars of years past.  What has Lionel done to make these a good value for operators since their first release?  Thanks.