High notes too harsh, can barely sustain long tones: is my embouchure the problem?

Hello everyone,

I'm reaching out for some advice. I'm currently struggling with my sound quality, which I'm not happy with. I find that my low notes sound pretty good, but my high notes are too shrill and not open enough. I play for 3 years on a Yamaha YTS-280, with a D'Addario Select Jazz 7M mouthpiece and Rigotti 2.5H reeds. I recently wanted to try Rigotti 3M reeds to see if it would make a difference. I'm still not satisfied, and I can only sustain a long tone for about 10 seconds… That seems very short given my setup. I think it probably comes down to my embouchure technique, which I've never had the chance to work on with the teachers I've had. To work on it, I came across this video: https://www.patreon.com/posts/how-to-fix-lower-148229508?utm_campaign=patron_engagement&utm_source=post_link&post_id=148229508&utm_id=d61420d8-70e9-44e0-927d-083567daecf0&utm_medium=email

I would like your advice on two of the exercises he recommends: the one at 2:13 and the one at 4:18. For the first one, I can't get any note out at all; all the air escapes from the top. For the second one, I'm slowly getting there, but it often jumps into the harmonics. Could this be an indication that I have poor embouchure technique? Are these worthwhile exercises to practice? Do you have any others?

Thank you in advance for your replies