Inter where left by Mourinho with a really ageing team mate, he effectively built it to dominate and get immediate success and buggered off to avoid the collapse and blame attached - Benitez was if anything an idiot for taking that job, they where 6th with two games in hand when he was sacked.
They where only 2 behind Barca when he was sacked mate, Athletico was ahead of both, and Real weren't the reigning champions - they had won nothing the season before with Ancelotti in charge, they won it the season Benitez was there for the first half of the season (and he qualified unbeaten through the group), he was sacked more down to the fans hating him than anything on the field in reality - and well it's Real Madrid ...
Chelsea finished 3rd mate with Benitez in charge not out of the CL spots
At Newcastle - they weren't clear of the bottom 3 when he took over mate, they where in 19th with 24 points out of 28, he got them 13 out the last 10 - so miles better.
2 Spanish league titles, 1 CL title, 2 Europa league titles, 3 promotions, FA Cup, Italian cup - comparing him with Koeman is miles off mate.
He is a very very good manager