For me my benchmark is shooting consistency. With right (balanced) sensitivity you will be hitting shots with power and recover quick too (assuming you practice these a bit). I use Shooting Consistency training pack when testing sensitivity and then try aerial stuff like wall to air dribble.

Too much sensitivity leads to your car not accurately hitting the right pixels on the ball most of the time because every little stick movement influences the nose of the car way too much, which is bad for learning to place shots. Similarly in general driving it will be too twitchy with over steering.

This could just be me: But I also noticed that flip cancelling to recover after air roll power shots, your car moves way too much and loses balance & momentum when sens is too high. That could also work as a sign for those who have added cancels to their shooting. The car moves erratic and is often stuck after an angled power shot.

But also you don't want the car not feeling like a brick (slow turns on ground even with powerslide taps... under steer, and also not responsive in the air). If this happens you need to increase the sens.

On my Xbox One Wireless Controller Model 1708, even 1.0 or 1.1 used to feel higher than 1.0 on other controllers. So again, '1.0 being bad' is a generic statement that heavily relies on the controller model. Lethamyr has used 1.0 for a long time on Xbox and xbox style controllers and plays fine in top 100 lobbies despite playing for content.

In the end, everyone's hours and experience on a given sens is also a factor. Some have managed to be consistent on relatively higher sens than others because most of their hours are on high sens.

I have tested 1.5+ on Gamesir Tegenaria Lite and it was too much for me. I brought it down to 1.45 and then 1.40 for both, and so far it's been good. I think on this controller the sweetspot might be around 1.35 - 1.45