I'm sorry, I wasn't making myself clear. The point I was trying to make is that iPadOS has a place as a next-generation OS if/when Apple decides that is mature enough to replace the Mac. I'm probably talking decades in the future given the snail-like pace that iPadOS is taken to get to where it is now (neither here nor there).
I'm not saying put macOS on the iPad. I'm saying make iPadOS as capable as macOS with the advantage of being a touch-first OS since the touch-first OSes are now the most used by people and that trend is only going to get worse. So in that scenario, if you want a MacBook-like experience, you would use a big iPad with a keyboard. If you want a desktop-like experience, you would pair the iPad to a big monitor.
Back to the 16-inch iPad: It's great that they make the device, but if iPadOS doesn't get better than what it is now, it's just a waste of time and money except for designers/ilustrators. So, I agree with you, it wouldn't be a great investment given what the OS is now.
And by the way for people saying it's too heavy: Just because it's a big iPad doesn't mean you are going to use it as you use the smallest iPad, sitting on the toilet watching videos. The point of a big iPad is to have a huge canvas, not to be used as a light-travel thing. Just like a 16-inch MacBook Pro isn't designed for light-travel. You would use it sitted down at a desk. People were saying similar things when the 12.9-inch iPad Pro was launched.