I just upgraded Kali OS and with it new Plasma KDE. Normally I open System Monitor and put it at the bottom of the screen about 3 inches high. I slow the history to cover as much time as possible. I cannot do either with the new System monitor which takes up a mandatory 2/3 screen height. I cannot find any way to slow the graph speed. It is hard to believe these settings are now hard-coded.

Can someone suggest a different separate system monitor, or how to downgrade to the past System Monitor, or adjust this System Monitor to have these features of the older utility?

You should have the previous one available to install - KSysGuard, unless your distro has removed it for some reason.

I know you can't shrink the page as much as you want, but if you use the Edit Page feature, and click on various elements, the new one is actually a lot more customizable over all. Except the minimum height

I experimented with this, and could remove titles bars and even adjust the height settings for different blocks in the history, but alas, the main window stays too large for your usage.