That is not true. I own a switch and charge it just fine while docked using a combination of This generic USB-C Hub (you need to make sure the hub has a USBC power input like this one does), a generic USBC cable (rated properly to do high wattage of course) and This generic AC adapter. No Nintendo dock, cables or charger needed. Since the usb hub and charger are so small, its my portable dock solution (and I have a short 1 foot HDMI cable I bring in my travel case too.

That's because it's all about watts. USB c cables have ratings. Some can do 5 watts, others can do 100. Assuming you have a high quality cable, now you need to worry about the charger. Some do 5w (older chargers) and some do 100 (ultra beefy laptops). The Nintendo switch needs 18w to run in handheld mode and 39 in a docked situation. So assuming you're playing docked, you want your charger to be at least 39watts. If you're just trying to charge the switch on its own, at least 18w. If you plug the switch into a 50 watt charger but only use a cable that can do 10w, then you're limited to 10w. And 10w is not enough to charge the switch.