So some here are assuming that when level 2 charging, 80% of the circuit capacity is always used. It isn't necessarily so. I have two 50A circuits for EV charging. I have my Model 3 and Y set for about 20A because that's all that's needed when charging overnight. It's easier on the grid and generation too. We typically only charge on Sunday and it's enough to take us thru the week.
I was doing the same thing when I first got my car. Charging at a lower rate means less heat in the wall charger and cable, etc so I assumed better. But several people mentioned that it's more efficient to charge as fast as you can because the car has to run some background loads anytime it's charging such as fans, pumps, the computer, etc. The less time that you can have those things running, the more efficient your overall charge will be because more of the current will be actually going into the battery. Now I charge at 32A even though I could easily get by with 16A for most nights.
When I charged at 40A (I have Gen1 UMC) the #6 Romex in the hot attic got pretty warm to the touch. I did not like that so I backed off to 30A and the heat is undetectable. Though there are loads that run during charging, there is also losses in the wire and the batteries that may reduce the optimum current for efficient charging ie using the fewest kWh from the grid to put the most kWh in your battery.
You say this as if one thing disproves the other. That's not so. Those are two true things, which are two separate topics. Using your charging equipment at its maximum level every day and creating that heat is a lot of heat cycling from hot to cold to hot, etc. very often. That is shortening the life of the equipment. With electronics that kind of heating and cooling causes metals and connections and solder points to expand and contract as the metals change temperature. That eventually stresses the metals and can make them degrade and become brittle or break connections. Also, there are the things people have mentioned, where sometimes these products are built to just barely function and pass running at their maximum level, but over the long term, for years, that heat can eventually burn and melt things. But that is a different topic than how is the efficiency and energy lost in the charging cycles. And that doesn't have to be an all or nothing situation. Sure, charging at very low levels, like 120V and 12A is going to be very wasteful. But if you are using a 240V outlet and maybe running it turned down a little bit, to 26A instead of 32A, that is saving some heat, but still pretty decently efficient.
If you are charging overnight, it is most always going to get enough charge, even if lowered to a rate where all wiring is cool to the touch.