Surely you'd admit he'd helped him mentally compared to his first 3 slam finals where he brought the lube especially the third one- I thought he'd get routined by Djoker at last year's AO semi but the closeness of the match (one he could have won) was a huge turnaround. Without Lendl, he'd have probably been routined in both Olympic and USO finals.
Yeah, the SF against Djokovic last year was a really, really important match in Andy's career. It was the first time* that he really produced against a top player in a Grand Slam match. If any doubts had crept in that he wasn't quite good enough this match dispelled them.
* before anyone points out that he twice beat Nadal in the latter stages of a Slam, those matches were no where near this in terms of quality and didn't require him t dig deep like this one did.