Wedge head design with plenty of squish, as in the old Chevy small block heads, was indeed to allow higher compression ratios. But Chevy switched to an "open chamber" design a long time ago on that engine to get better breathing. Then there's the Hemi, which has no squish area at all, and the 4 valve pent roof chambers which have a negligible amount of squish.
The idea of squish, to increase turbulent mixing in the chamber to compensate for uneven fuel mixture distribution, has pretty well been negated by the switch to closed loop electronically controlled fuel injection.
Or a Hemi, which also has the plug centrally located.
But this doesn't really help the detonation problem. The old Hemi's needed higher octane fuel than the old wedge head engines. The speed of light is still a lot faster than the speed of the flamefront, so the radiant heat of the initial burn can still pre-ignite the mixture at the periphery of the chamber. When the two opposing flamefronts then slam together, you get knock.
Most dual plug setups also have different timing for the two sparks, one leading, the other lagging. This is mostly to try to better burn lean mixtures. In other words, it is mostly an attempt to get better fuel economy at light load.
The real answer to why the latest engines can run nearly as high a compression ratio as engines of the 1960s is closed loop electronic controls. The mixture is always right, and even, the spark timing is always right for the engine load and RPM, etc.
Gary