Have you tried Flap Wheels Grinding Sanding Discs, they are pretty good.
Yes, I have a pile of them on the shelf. They are vicious and remove material fast ! I used them to grind down the tabbing on the old I/O engine mounts and stiffeners. For doing the large flat areas I like the bigger diameter 7" makita. I seem to end up with less "smiles". My go-to on the deck, to prevent too much unevenness, is the proter cable random orbital 7335. I have about 20 yrs on it and it's tired but the dustless feature works really well.

