For a layman like me, it looks as if it already has a flame diverter. The rocket stands so high above the ground that flames go down and spread to the sides, but it was not enough.
The main part that may be missing is a flame deflector, a kind of inverted 'v' structure that would redirect the momentum of the exhaust to the sides (where a horizontal concrete slab might redirect it back up to the vehicle). With the vehicle up on the OLM you could maybe also make the deflector 3 dimensional and build a sort of inverted cone. Spreading exhaust in all directions could disperse the energy more quickly, although I'm not sure if you want to necessarily redirect exhaust toward, say, the tower base or the tank farm.
If they add both a trench and a deflector that gives them some degree of control of where the exhaust goes once it leaves the underside of the rocket, so you could lead it away from critical pad infrastructure and direct it out to some empty area to disperse. Obviously all that requires quite a bit of space, which they might not have available.
The other part that was missing was a water deluge system (it has some - see below). With the water deluge, it would help muffle the sound (currently 6 miles away gets windows blown out) and make it harder for any material that is kicked up to go anywhere (up or out) as it would also have to go through several hundred thousand gallons of water too.
I think the problem was that the big concrete pad needed expansion joints. Those joints should have been angled such that when the pad is in use the venturi effect caused the concrete slabs to be sucked towards the ground.
However, this wasn't the case - the joints were vertical (as would be normal for laying a parking lot), and the end result was exhaust gasses went through the joints and lifted the slabs up, causing many of them to get blown away.
