With all due respect, I completely disagree that Smalling was a world class performer last season. I'd describe Smalling's performances as like I stated in the post you quoted. Generally solid performances from a player who has progressed reasonably well in the last 2 and a bit seasons.
IN all my time watching United I have seen 3 genuinely world class centre backs in 32 years those being Nemanja Vidic, Rio Ferdinand and Jaap Stam. Those players were world class because they played to a consistently high standard and did it against the best players in the Premiership and the Champions League. That's my own standard of a world class performer. They perform over the course of a whole season, not just for half a season. I'd be inclined to also put Paul McGrath in that category as well but he had well documented injury and off field problems but when he was fit and motivated he was a magnificent centre half. That leaves players like Bruce, Pallister and Johnsen who were in my opinion very good players who I would not describe as world class.
I regularly watched all those players I referred to above. La Liga is very readily available in the UK as is the Champions League and Europa League to anyone as was the European Championships.
I don't really understand how Donald Love could have caused Smalling that many problems considering he only made two appearances, one as a sub and another a start in the Europa League both in the second half of the season. Not really a highly significant factor. As far for Rojo, when fit, he was our first choice left back last season but missed a fair few games with injury.
The idea of a world class half a season is a fairly odd concept. To me what makes a world class performer is the ability to consistently put in top class performances at the highest level which means doing it over the whole season not just half. Personally I'd be looking for at least two top class seasons before placing anyone in that category. Even during this first half of the season run United lost to Swansea, Arsenal, PSV, Wolfsburg, Bournemouth, Norwich, Stoke, and were knocked out of both the League cup and the Champions League.
You are going have to describe to me your idea of a world class performer as our ideas seem very different.