This match up always feels like Dhalsim vs Zangief to me, yes it's true he covers a lot of range. But you only need 1 good read before you get in, doesn't help Superman that his wake up options are pretty poor.
Make EVERY hit count, Grundy has 40%-55% combos 1 bar for this exact reason.
Don't bother using Swamp hands unless you know he's gonna ground laser on the floor, not worth the MB.
React to all his jumps with a dash as someone else pointed out.
Don't try to run away after you have a life lead, you're gonna end up dying to his lasers eventually (I tried it 3 times already, doesn't work.)
His air to airs beat yours, but I'm pretty sure an early j.1 beats most of his options in the air.
the air dash is a trick fuck. He has some weird recovery in the air, but at the end of his air dash, he can do a ground laser/dive kick.
He has a 8 frame f+2,3 string which is...-2 on block, and can cancel that into super breath for +1
All about patience, time your dashes, and slowly if possible push him into the corner.
I actually enjoy all of the zoning matches from Grundy, cause not only is it fun to chase someone down, but it actually shows how patient and how much training you've put into these matchups.