Mixups mixups mixups? Your grab's purpose is like 80% to beat shields. If you don't grab, there is basically no reason for the opponent to not just sit there shielding your approach and catching you when you finally do something predictable or unsafe. Pound by itself will not break a shield either, so don't think approaching a shield with Pound is going to scare them to drop it, and it's unsafe on shield so hitting it is pointless unless you can miraculously follow up. In order to break it you need safe shield pressure first, like a well-spaced dair or bair.
And if the problem is that they shield your attack approach, you can always just approach but not attack. Approaching the same way every time just makes you predictable and you won't get anywhere. Run up and empty hop to bait a response, and then punish accordingly, because either they're going to do something or they have to keep holding shield. Meanwhile, you also have to be wary of which character you're fighting and how you should space yourself so an empty hop doesn't get you smashed in the face. Ideally you'll be as close as possible while being just out of range of whatever they pull, which is often close to their roll distance, which is also often close to their dash grab distance. The only crappy thing is that we're slow on the ground so our dash grab is iffy.