all chars can grab and so all players must grab
I think you're assuming a bit much about all players. Or skipping a few steps.
Positives about a standard grab:
unblockable mid
can change your/your opponent's position
slows the game down for mental planning, I guess
Negatives about a standard grab:
can be broken 50% of the time by the opponent
can't grab jumpers/crouchers
limited range
If you play a character who only has a standard grab, chances are that character's playstyle revolves around using mostly mid/low mixups, or strong mids/highs mixed with grabs so they don't always block mid. Mitsurugi and Taki use mid/low mixups very well, to the point where they can easily win matches without a single grab. Characters like Vader or Setsuka though have very powerful mids but lack good lows, so they'll grab more to scare the opponent into ducking more often.
Some characters come with a healthy balance of both grabs and regular attacks. Cassandra has good normal mixups, but also has a normal and crouch grab, so the player can switch between varying playstyles and still perform well on a single character.
On the opposite end of the spectrum, playing Rock pretty much requires you to grab whenever possible (since that's where most of his damage comes from). Rock has not only mid grabs, but crouch grabs and ground grabs too. If a Rock player can read his opponent well enough to guess where he will be most of the time, he can grab them out of any position except jumping. Astaroth can even grab jumping opponents with his A+G, as well as having crouch and ground throws, so they are strong tools for these characters due having more situations to use them.
To get back to why I quoted KingAce, some people can be 'too good for grabs.' It's all about your character, and how you choose to play them.