'they've lessened the size of the system'?
Wouldn't "lessen" work in terms of amount of something, but not size?
Although legal English I don't think I've ever heard "lessened" used in my 53 years of life. In this instance it would surely be reduced, decreased or maybe even downsized.
I agree. To me “lessened” should work here, too.
Czy mogę powiedzieć reduced zamiast decreased?
Why can't it be "We decreased the system size." ?
"we" is the wrong pronoun, but ok for "system size", added.
That should be "They REDUCED the size of the system". "Decrease" is not a transitive verb.
It's both transitive & intransitive according to Merriam-Webster:
I stand corrected, but it still sounds odd to me. Maybe a predominantly American usage.