Yes, Ambrose was stellar vs and in Australia. He averaged sub 20 in Australia. In what was the ultimate test for his era, he averaged sub 20 in 14 tests. Versus his no. 1 rival and the country in which he played the most he averaged just over 20 in the UK.
Pakistan was supposedly the most difficult place to bowl, yet over his career and even during his peak Imran averaged 5 points more away from home.
In the Caribbean, Imran was damn good, he wasn't stellar to the extent that Ambrose was in Australia. 25 isn't 19. Versus his number one rival in India he averaged 28. In Australia, even if one removes the final series as Subz demands, he averaged 27.
Over his career, and taking away his teenaged series vs England, the only country he excelled in was said England and minnow SL.
That's it.
That's not top 5 ATG fast or bowler period performances.
Imo he's not better than Warne, Murali, Ambrose nor Steyn. All those guys were at multiple points in their career the best in world.