To make my point clear: The scrollbar size is ok, but not all area of it allows to scroll.
The Mouse wheel is an alternative way.
(Also: The keyboard arrows can be used if you will select the element of the grid.)
Besides, using the mouse wheel solves the problem only with vertical scrolling.
The window can contain the report with a big amount of columns, so the user will be needed in the horizontal scroll.
(the Shift+Scroll combination is not trivial for a typical user)
"use a browser zoom ( Ctrl + mouse wheel) to increase all UI interface elements"
IMHO: is not trivial for a typical user too.
Maby the scrollbars annoyance can be eliminated by:
Moving them a bit closer to the centre of the window,
Moving the “Resize action zone” out of borders of the visible part of the window,
(for example, like google chrome window behaviour)