For users with small screens there is a big difference in accessing all UX elements in the dialog windows.
Please compare attached Classic and Lightweight screenshots.
On Classic all elements (read Pager) are always accessible by using the browser scrollbar.
On Lightweight the Pager is not accessible in Chrome and Edge. In Firefox a scrollbar appears in the RadWindow so the user can scrolldown there.
Screenshots are made with Default skin; as we use Material skin the problem occurs even on modern laptop sceens as the UX elements are all bigger.