I can't find in the manual where it says not to charge at a charging station over 150 kW. The Mach-E specs say it will charge at 150 kW peak, but that's not the same as saying not to charge at a station that can provide higher power. The car will negotiate with the DC fast charger to charge at the higher of the power it requests or the maximum the charging station will provide.
If you charge at a 350 kW charger you'll have a higher chance of actually reaching 150 kW peak charging rate.
In my experience if I plug in to a 150 kW Electrify America station I tend to peak around 120 kW but I get a higher peak (just over 150) on a 350 kW EA charger. I assume the 150 kW charger has a current limit below what the Mach-E would like to receive at low states of charge.
If you arrive at the charging station at a low battery state of charge you'll save a few minutes of your time by plugging into a 350 kW unit than a 150 kW unit. If you're above 50-60% charge the higher available power won't let you charge any faster because the car requests lower power as the state of charge of the battery increases. Above 80% it drops like a rock so at that point you're mostly tying up a charger...
