I've been playing for about a year and a half now. I work lip trills every practice session and I've definitely noticed how notes like 2nd line G and 3rd space C have become much more effortless. As long as my corners are tight, embouchure firm, I can play with very little strain. But it seems like there's a difference between everything 3rd space C and below, and everything above, especially D to say A etc.
My question is, should I ever expect notes in that range to become effortless? Or do even pros have to add extra strain, that's just the nature of the beast so to speak, to get into that range?