I don't have a problem with you or anybody using program mode or any mode for that matter, as long as you are consistently capturing the exceptional image ... The image you previsualize ... The image you seek.
Yes, for many genres of photography, speed is not only important, but critical. To be fair, I've never used 'P' mode, so I cannot speak from experience. But, to my mind, going 'P' is a step up in complexity from 'M' in attaining the exposure you need/desire. Practice and experience goes a long way to increase speed.
For at least 3 decades now the camera engineers have been working on this one. You and I both got started doing this prior to that time. My first serious camera came with an option to have a meter in the prism or not. We learned what worked for us then.
My job however required me to teach the younger generations -- I've always had to deal with the question, "What does this knob do?"
The first assumption: Whether M, P, A, or S you're going to use the meter in the camera.
In M you directly select a shutter speed and f/stop (both require physically pushing or turning something) and at the same time you're paying attention to a meter read out. You've assessed the lighting condition and are deciding that you want the exposure plus or minus or zeroed on the meter. Let's say you select 1/250 sec. shutter and then adjust the f/stop till you get +.67 on the meter readout. For the sake of illustration that's f/6.3. Let's assume your camera is a 5DmkIII. You have to turn one wheel to set the shutter and a different wheel to set the f/stop. Exposure is 1/250 sec. f/6.3.
In P mode: The shutter and f/stop are now automatically set by the camera. You make the same lighting assessment only this time you turn the EC wheel to +.67. Looking through the viewfinder lets assume you see 1/60 sec f/13. You turn the program shift wheel to change the shutter speed to 1/250 sec. and the f/stop of course changes right along and comes to f/6.3. Exposure is 1/250 sec f/6.3.
On the 5DmkIII the wheel you turn to set the shutter in M is the program shift wheel in P, and the wheel you turn to set the f/stop in M is the EC wheel in P. So physically you're doing the exact same thing in both cases and arriving at the exact same exposure result. It gets hard at that point to argue that doing the exact same thing to get the exact same result is better done one way or the other. It's only different in your head.
But, the big but, speed alone doesn't make up for a wrong/bad exposure. (But Photoshop will ... Back to digression.) I think you need to shoot a bunch of weird/tricky/bad lighting stuff in Manual and in Program and see what works best for you.
Exposure is the photographer's job. P, S, A, or M along with the camera's EC adjustment all make it possible for the photographer to get to the same place (first assumption applies). Using P mode the photographer can hand exposure control over to the camera but there is no requirement that makes that so.
Joe
How do you shoot ... Typically I shoot M with Spot Metering. I meter off a subject with a known value, grass, skin, et al, then make my compensating adjustments, focus, reframe and release the shutter.
I need to play with the EC and P ... Just to see what it does.