The Steam Deck and Steam Controller (2.0, but w/e) use Voice Coil Actuators spread throughout the device for both haptics snd rumble.
They're both measured/set in decibels.
https://www.electricity-magnetism.org/voice-coil-actuator/
It could be that you've found something actually worth posting a bug report about on... well I'm not sure where lol.
It could be a Steam Input issue, it could be a Proton issue, it could be both.
It might be the case that the style of command the game sends is basically 'formatted' in such a way that its not being properly interpreted/translated the way it would be by the kinds of controllers the game was/is specifically designed to work with.
As far as I can tell, while the Steam Controller and PS5 Controllers use VCAs... the Xbox One Controller uses a more old school, 'eccentric rotors', unbalanced psuedo wheels that spin on an axis.
So... for a system like that, a straight pulse of linear input command would feel to get more instense, and then gradually taper off.
If you give that ssme input to a VCA, it ... 'interperets it literally', if that makes any sense.
Its kinda like VCAs are digital, and ERs are analog... sorta.
So... there would have to be some kind of ... additional emulation required, basically, to translate rumble 'commands' that were made to work with an ER system, to a VCA system.
Like uh, 2 seconds of ON would have to be translated into an accumulating VCA amplitude, that would then taper off after the ON input ceases, some kind of buffer.