Qwt can do some algorithmic workarounds to avoid doing unnecessary stuff, but in the end it is Qt that is doing the rendering. So I'm afraid there is not much Qwt can do here.

In case you are on X11 I recommend to use the hardware accelerated X11 paint engine. ( export QT_XCB_NATIVE_PAINTING=1 ) instead of the homebrew raster paint engine, that is enabled as default.
On Windows you can go with OpenGL, but according to the docs it does not seem to support AA_EnableHighDpiScaling.

By the way: did you check which of the flags is hurting most ?

Uwe