I tried that as well, Old line weights just show multiple lines of weight 1. So a line width 2 would be three equally spaced line weight 1 lines. line width 3 would be 4 equally spaced line weight 1 lines.
I am still horribly frustrated by this problem. I've tested it on 10 monitors and 3 laptops. All of them had the same issue and all of them had resolutions greater than 1440. I had to buy a specific 21" 1920*1080 monitor to get the lines to be readable. You can set the resolution to be much lower but then you lose the native screen resolution refresh rate. (on a lot of monitors anyways)
Going forward, this is probably going to become an issue for your software as almost every modern computer comes with a ultra resolution monitor. (unless I am just an outliner).
Oddly I also ran into this issue with a coworker's 1600*900 monitor at their house.
You really need some sort of graphical display only line thickness setting.