It does work better to start with the impact driver before the screws are chewed up.
They can be safely used with delicate aluminum parts. I've done it hundreds, maybe even thousands, of times on aluminum motorcycle carburetors. The trick is to use a sharp rap rather than pounding on it.
One of the reasons an impact driver tends to work well on Phillips screws is the included bits (at least in the ones I've used) weren't actually Phillips but were JIS. The Phillips screw/driver combination was designed to limit the amount of torque that could be applied. The driver actually climbs out of the screw head as torque is applied. My understanding is this was done to prevent over torquing on an assembly line.
The JIS is very similar to Phillips except the screw/driver have a different shape at the tip so they don't push apart with torque. A JIS driver works fine in a Phillips screw and is less likely to climb out of the socket. The reverse isn't true. Phillips drivers perform poorly in a JIS screw.
JIS screws typically have a punch mark on the head to indicate they're not Phillips.
The only place I've seen JIS screwdrivers is McMaster-Carr. I suspect they can also be had from the big name too trucks. But as I said, the bits with the impact drivers I've owned were actually JIS.
I wonder if Ford used a JIS screw on that throttle body. That would be a bit surprising because it's typically the Japanese (Japanese Industrial Standard) that use them. U.S. products tend to use Torx heads.