>>2044804
>>2044805
To add to this: seems like it wasn't totally crazy of me to assume this would work given that this has been sold as such elsewhere
https://barquebike.com/products/sl-m4100-rd-m4120-m5120

One final remark about my experimentations: I even went as far as significantly shortening a chain during testing
It was so short that it would no longer be enough to switch into the largest cog in the back
This would put the derailleur chain tension pivot under more pre-tension
The effect of the upper chain run bunching up when freewheeling after pedaling persisted
The chain would be even longer if I used this derailleur and the 11-42 cassette (as the specs say) with a front derailleur setup, which would mean that a >34t chainwheel might very well be installed which would mean even less tension meaning even more chain bunching

No matter how I think about it, this seems like a faulty product
And it doesn't seem counterfeit either