As I think you’ve found, adding too many landuse=grass areas can be a bit much!

landuse=grass is meant for areas which are just grass and have no other use, such as verges, central reservations, etc. — see https://wiki.openstreetmap.org/wiki/Tag:landuse%3Dgrass

In most other cases, it’s better to tag the area for its use (e.g. cemetery) and then add surface=grass or landcover=grass to refine the rendering. (Sometimes it won’t change the rendering, but the data will be there at least.)

Hope that makes sense, it’s a little bit fiddly :)