There may be a perspective issue here.
Anyone who flew the TriStar for two decades with the RAF did so, for most of that time, in a service whose other large aircraft had their design roots in the 1950s (VC10 and C-130) or 1940s (Nimrod and Belslow). 1968-launch technology looked pretty good by comparison, I'm sure.
Conversely, if you worked on TriStars in the civvy world at the same time, your benchmarks were increasingly set by post-ETOPS twins with better reliability and onboard diagnostics, and the 747-400, which incorporated a metric eff-ton of lessons from earlier versions. In which case the TriStar could seem a little dated.