But the rail station reaches the best point it can to serve all 3 terminals. It would be great if you could get heavy rail to the doors of all terminals, but, that's a pipe dream.
I found the walk from T3 to the rail station no worse than the walk from Heathrow central to T3.
As for the buses, we need to be realistic, there aren't going to be buses to all corners of Cheshire and Manchester.