I have seen the following meme go around Facebook several times:
As a horn teacher I have to say this meme, while it sounds like good advice, is very wrong.
Sure, long tones are important, but only to a point. Yes, it is a skill to master. But essentially they are weight lifting for your chops. They end up being a part of many warm-up routines. The reality is I rarely work on long tones after the first minute or so of my warm-up routine. It is not as though you can’t achieve the same effect of training your lips by playing real music.
A mouthpiece change however can make HUGE differences in every aspect of your playing. It can take you from sounding like a good student to a pro in literally an instant. It can improve your tone, your high range, your low range, your endurance. Everything.
I really worry about teachers who don’t actively work with students to search out a better horn and a better mouthpiece, as both hugely impact the ability to reach a high level on the horn. Telling students to do long tones in this instance is just lazy teaching, ignorance. Some horns really need a European shank mouthpiece to focus the high range, for example. There are so many variables to balance and you can only get there through thoughtful, guided testing.
In short, no teacher can inspire your high Bb to speak better if it is just a bad note for your combination of horn and mouthpiece, and long tones alone won’t get you to the highest level of horn playing either. You need the right equipment.
And mouthpiece choice is a topic I think most horn students intuitively know is an important one, as one of the most popular article series ever posted on this site is the below by Bruce Hembd, on choosing a French horn mouthpiece. Get reading, there is a lot of information on the topic in Horn Matters.