Embouchure changes are big things, just like you mentioned, and the time to be making them is not generally at the point of highest stress and in the absence of several informed opinions with direct knowledge of the specific player. I'd be especially leery of any advice to FIRE my lesson instructor and strike out solo from someone who hasn't met either me or my instructor.
To the OP: Yes, you should consider if your lesson teacher is giving you the best advice, and it never hurts to get a second opinion if you are worried a piece of advice is potentially not the best for you. You also always have to weigh what they want you to do against your own "feel" of whether something is working or not. That said, often the person with the most intimate knowledge of your playing is your lesson instructor, and that should be taken into account more than any of our posts here on the internet. If you are worried, ask your band director or find another player to take a lesson or two from. They will be able to look at YOU and listen to you play, and thus provide a much more informed perspective on if the embouchure change may be playing a role in your struggles.
To me, the most important quality any lesson teacher can have is the ability to make you accept where you are and give you hope and a method to get you where YOU want to go. If your instructor can inspire you to practice and work with you to identify what YOU want to accomplish in your playing, then great. If they seem most concerned with remaking you in their image or you find you don't ever want to practice after they get done with you in a lesson, then you might consider a change.
Either way, don't rush to drastic measures like firing instructors, switching your embouchure, or giving up the horn based on a post or two here. Be patient, build some confidence, and get some more perspectives from people who KNOW YOU and your playing.