Very,very few tractors have down pressure on 3 pt hitch. Belarus is one brand that comes to mind that does plus some old Farmall's(IHC)
Yeah, down pressure on a 3PH really doesn't make sense in most situations. There is a tendency to lift the rear wheels and lose traction. But on to the subject at hand.
3PH discs are made fairly light so they can be lifted up and down without raising the front of the tractor when lifted. Granted, the guys that have put weight on their 3PH discs likely haven't had an issue. A FEL or a gang of front weights can help.
Discing after a rain and going slowly is an option that may help in your situation. 4WD is a necessity.
Second point: Be careful of sharp turns or setting to maximum "bite" of the gangs. I added weight to a 7.5' 3PH disc and promptly went through four disc bearings.
Lastly, the suggestion of an offset pull disc is a good one. They seem to do a better job of leveling and turning the soil. They are heavy enough to get right down to the axles in just a few passes.
OK, one more. Consider a plow. A plow can make quick work of a pasture. Then going over it in a few weeks with a fairly light disc is a breeze.
EDIT: Darn, just thought of one more. If the grass is not too long a box scraper with the scarifiers set to full length can rip up the ground enough to allow the disc to better penetrate.
OK, I'm done (for now

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