More commonly known as the placebo effect.
I know what you're talking about, years ago I thought the same thing. I think it's common, particularly with all the hype and marketing surrounding synthetic motor oils. The advertisements want us to believe that everything is better with their premium oils, and our brain wants to believe that after forking over more cash for better oil. Unfortunately it doesn't actually work like that.
Think about it...if lubrication was holding back a noticeable amount of engine performance, imagine how much friction would be occuring? You generally won't feel one or two horsepower, and if you were losing more than that due to lubrication your engine would self destruct in feet, not miles. There would also be a tremendous amount of heat generated by said friction, and the engine would get HOT.
I've switched between dino and synthetic oils in lots of cars and trucks over the years, and it makes no difference. I'm sitting in my '15 F150 at the moment with a very similar engine to your Transit, and this got Mobil1 just a couple thousand miles ago for the first time in place of the Pennzoil conventional I used before. Didn't notice a bit of difference, it runs like the same F150 I drove off the lot with Motorcraft conventional 8 months ago.