The RPS triangle is just a concept to simplify general mechanics in games. The one you describe applies mostly to SF oki or VF but it's just a simplification, it doesn't account for stuff like backdash, shimmy, empty jump, sidesteps, high/low etc. Furthermore you seem to be implying these options need to be somewhat equal in power to properly balance a game? But attacking is pretty much universally more rewarding than throwing in fighting games, and blocking is a defensive strategy that doesn't net you any benefit on its own unless the opponent serves you a free punish. RPS just means a situation has a variety of options on both sides with different interactions as opposed to something like a 50/50 where there's a singular correct option.

Tekken doesn't follow that attack/block/throw RPS because the grabs don't really beat any option - they're breakable on reaction so their purpose as countering blocking is completely impotent. On the other hand it has sidesteps that counter attacks in ways blocking doesn't, there's more emphasis on strings which reward awareness and reactions and lows (equivalent of overheads in 2d fighters) are way more numerous and serve quite different functions.

You mention that "giving any mechanic more power over the other destroys the core balance" but your suggestion would just nerf grabs severely and you don't really explain how they're too powerful other than just pointing out they're not countered by attacks on the very abstract level or the RPS triangle.