Eh this is mixing a lot of different limitations.
Older, lower capacity cars like a Bolt and Niro cannot charge as fast, but that has not much to do with the voltage. Yes they accept ~400V as input, but the pack itself limits power to a low level.
Then there are 400V cars that accept up to 3-500A, for 120-200 kW of total power. These are common and include all Tesla's (ex that new model that has almost no sales / is barely a rounding error in delivery count), VW MEB based cars, etc etc. The new 2025 Model Y LR is 250 kW peak, 124 kW average, 10-80% in 27 minutes on a 250 kW V3 supercharger.
There are 800V cars in the wild, mostly Kia and Hyundai, but also some Volkswagen Group Premium Platform Electric, Audi and Porsche. These can use 800V x moderate amps to reach a higher total speed. But most chargers installed, like Tesla superchargers up to V3 (250 kW), are all 400V. V4 finally adds 800V / 325 kW but it's just a bit faster than before, not a huge difference and not like doubling the voltage doubles the speed.
The 800V Kia EV6 SR charges from 10 to 80% in 18 minutes on 800V, 22 minutes on 400V / 150 kW, that's not really a huge deal. More important is the battery itself - the battery can sustain the high 150 kW rate for almost the full charge. Slower cars at the ~30 minute mark for 10-80% can only handle 100 kW of average power, like the Enyaq LR, 10-80%, 114 kW, 28 minutes.
To summarize, there are three groups of cars
1. Slower, older models that cannot fully utilize a pretty standard 150 kW plug.
2. Default group that can charge up to 150/250 kW but usually hang around 100-120 kW average, for top up in 24-30 minutes.
3. Fast charging cars that can use a higher power connection up to 300 kW for a charge in ~18 minutes, but if and only if on a 300 kW / 800V connection and no second car plugged into the stall.
