I don't "come up with" the "complicated lingo" that I use. It was part of the curriculum for my aerospace engineering degree. And the "lingo" I use here is the usually the simple version.
As for the rest of it, a fan shroud significantly improves the efficiency of the mechanical fan. Same reason that little gasket on the hood that sits on top of the radiator support makes a difference. If the fan is effectively sealed it pulls air evenly across the entire surface of the radiator. If it's not it doesn't, and without a shroud (or a hood seal) you're losing air around the radiator and fan. That's less efficient, simple as that. If you want to believe a dude at a radiator shop over an aerospace engineer about air flow, hey, knock yourself out buddy. Not my car, not my problem. Same for the fan out in front of the radiator. It absolutely disrupts the flow of air when it's not running. Sure the car might not overheat, it's not blocking everything, but you're losing efficiency everywhere and that's all just parasitic loss. Much better off with one type or the other. Pretty much every new car that rolls off the line nowadays comes with an electric fan and a 100,000 mile warranty. If they weren't reliable they wouldn't be there, the factories wouldn't want to lose money replacing them if they were constantly failing. Belts still break on mechanical fans, rivets fail and send blades into the radiator, water pump shafts fail or eat bearings, clutch fans stop working. All of that results in the same thing, no fan. At best. Popping a relay and losing the fans on my car doesn't even necessarily mean I'm dead in the water as long as I keep moving. Traffic won't work, but my fans almost never run when the car is going over 30mph.
As for the electric fans, if you're doing it right you're adding a higher output alternator, which is probably heavier. Plus the heavy gauge wire for the fan. Plus the relays. Plus the fans. It's not a ton of weight and it's not super hard, but it's all uneccessary if you can get by with a properly set up mechanical fan. And if you're not adding relays or alternator then you're either not pulling much in the way of amps, whichs means you're not pushing enough air to be worthwhile, or you're putting your stock wiring at risk. But you're not even running a temperature gauge that shows degrees, so, how would you know what temperature your engine is running?
Those infrared thermometers read surface temperature not coolant temperature, and the way the ir works the indicatated surface temp varies by material and even the reflectivity of the surface (i.e., painted metal will read a different temp than polished, rubber different from metal, etc).
Believe whoever you want. You think because what you're doing works it's the best way to do it, but I can assure you that's not true. Maybe the car stays cool enough and that's great, but you're losing efficiency, and that means lost power. If you're good with that, awesome.
