I disagree with this. Wii U was simply better built, designed better. Gamepad and Pro Controller had good ergonomics and worked well, good sticks, good d-pads, the charging stand for the Gamepad fits perfectly, Pro Controller has excellent battery etc...
Outside from the main tablet which is okay on Switch, everything is cheap and prone to issues. The stand is garbage, the console wiggles inside it. The rails to put the joycons will get loose after enough use. Sticks will drift. Joycons will disconnect. Joycon quality is bad, with super cheap plastic. The button layout on the joycons is abysmal because they wanted to have them usable as individual controllers. D-Pad is a complete joke. Pro Controller d-pad is awful as well. The piece of plastic for tabletop mode is ridiculously small. HDMI cable is super short too.
Unboxing a black Wii U really felt like having a good quality product, with everything that was well thought out. The Gamepad doesn't have the best quality screen of course and really that's the only thing were Switch feels better, but being a handheld at heart, it was the least it could do. Gamepad was still good enough as a secondary screen, and really nice to play all the retro games from the eShop. GBA games look very good on it. Unboxing a Switch feels like opening a toy. I was there day one for both systems.
Gmepad had the full sized controls. But it wouldn't work for them as a pure handheld. IT's too big and a bit clunky. It also had the luxury of not having to run games natively so it weighed much less than it would if it were a true handheld.
You really need to compare Switch to 3ds I think. Handheld to handheld. That's really where it was much improved including controls.
And I like a lot about the joycons. The buttons are super clicky and my thumb covers all 4 so I can easily hit any button without lifting my thumb. I like the speed that gives with minimal effort.
The joycon sticks... also are more responsive/quick in practice because they have a shorter throw to full throttle. The downside is they are less accurate/precise. If you're walking on a ledge ...it's much more iffy with a joycon than the Pro controller.
I don't like the joycons as mini-gamepads. Too tiny. And the 2 buttons in the front when sideways are too mushy with the straps or too hard to press without.
I was bugged by no dpad but I haven't thought about it at least in recent memory. I guess it does the job good enough.
The bumper buttons seem a little sensitive on the joycons. They seem to activate accidentally for me too often. Maybe just due to the small size (of the controls) that I accidentally can't help hitting them sometimes.
As far as the rails, yes the whole thing is less rigid due to them. Tradeoff to having detachable controllers. We have a Switch Lite too and the one piece (rigid) controls and the dpad are 2 of the positives over the Switch.
But there's room for improvement next gen. I don't know if they can go full sized controls or not. Maybe they can do multiple skus. Gets expensive to have to buy a Pro controller too. I don't know if they can get away with that tax again so soon. lol.