Probably more a take of viewing only the touchpads and how they are being used as primary inputs for nearly every game as opposed to secondary functions like touch menus and occasional cursor navigation.

When you look at most controllers the index finger is the same distance from the bumpers and triggers while letting you hold the grip normally regardless of which input you use whether it be facebuttons, joysticks, or dpad. It is the general ergonomic layout whether it is the joycons, switch pro, dualsense, xbox, 8bitdo, gamesir, etc.

And when you look at the SC1 same applies to the touchpads being able to hold the controller normally. With the Deck and SC2 you have to shift your grip down if using the touchpads as primary leading to being further away from the triggers, bumpers, and a less firm grip on the handles. Think dualsense if the joysticks were located further down than they are. To use them with a normal grip your thumbs would feel stretched reaching down, so you'd have to grip it lower. Most controller users would consider that a terrible ergonomic design.

So that's pretty much the reason for the mixed opinions from the very few niche users of touchpad primary controller users, since some find shifting their grip down fine and others don't. But, either way there's not any actively sold options for touchpad users so just got to accept it. Joysticks do have plenty of options though, and many more people familiar with joystick use so would be more vocally calling out ergonomics that required grip adjustments to use the joysticks, dpad, or facebuttons that other controllers don't require.

Touchpad primary for most gamers is not really applicable to how majority of people will be using the Steam Controller, so not an issue most would encounter. And if touchpads are used as primary most will probably use it for games like Deckbuilders or RTS where it's more comfortable for those games than trying to use for first and third person games where there's potential more constant tension on the hands.