I have agree with what you've said here. Me and pressure had been good buddies for a long time. However, now he just don't come 'round very often (and I don't miss him either!). It makes a big difference in your trumpet life when he's a stranger.
How much pressure is too much? How much is enough? Well, my definition is, if your upper lip feels kind of sore and looks a little swollen after you play.... You're using too much.
If you can play about 1/2 dozen notes above high C and that's it, your chops are gone... You're using too much.
If your teeth feel sore after you practice... and the next day..... You're using too much.
If your upper lip doesn't feel good after a practice no matter how long you've played... You're using too much.
If you try to go above the staff and you get this weird sound from air leaking around your mpc.... You're not using enough or you haven't developed the right muscles enough.
I've read and heard all the trumpet-on-a-string ideas. I've tried a few with much frustration. You make a good point. They are practice routines. But, nobody tells you what they are designed to teach you except to use less pressure. They don't tell you what you are supposed to learn from it or how to get rid of the pressure. Pressure is a result of not being able to adjust your embouchure sufficiently to achieve the range you desire. Trumpet-on-a-string may help you to relieve the pressure but you need to get other things working to replace what you used to use. Using your air as support for your chops (easy to say, but you've really got to feel it to believe and understand it IMHO) goes a long way toward relieving arm and "throat" pressure. Adjusting lips, tongue level, and oral cavity; all of these, for each note. These are the things that trumpet-on-a-string might be used to teach. But just as important, is the freedom from tension. It can kill all your efforts in other areas. You're right on when you say you won't even think about pressure when these things are working correctly. You will feel a strength in your chops that that will make you think they'll live forever. You won't get the urge to mash your lips to get the notes.
Going to the extremes; playing the high range, or using no pressure can actually cause you to strain your neck and throat muscles in a no win attempt to compensate for other things that aren't working. In a way, tension *is* a sort of pressure. Pressure that becomes a self-fulfilling prophesy that the high range is hard to play.
When you go from using pressure to making your chops and air work for you, you will be working muscles that likely didn't get much of a workout before. When they get tired, you'll want to keep playing anyway. This will make you revert to pressure again. Stop and rest. If you don't, you'll subtract from any gains you've made. Please believe me. I got me some real experience in that area. You will gradually build strength and, more importantly, you'll build a set of chops that know how, and are allowed to do their work. Then, you can just play. :-)
Sorry to go on so about this but this subject really hits me where I live.
How much pressure is too much? When it keeps me from playing the things I want to play, *that* is too much.