Always been disappointed that Morgan couldn't transfer his best ODI form into his test outings. He's a fantastic player the way he can find gaps in the field. Regarding how long these problems go back, I agree that it goes back further than 3 months and the batting was poor in the summer. However, saying we've been on the slide for 5 years is a bit of an exaggeration too. We've completed 3 back-to-back Ashes series, won away in India and got to number one in the world in that time. Strauss's retirement started the period of transition but it didn't particularly become evident until the last year or so.
I don't think Morgan will be the man to replace kp - he's ok as a one day player but failed too often in tests - I expect them to look at younger batsmen and it may take time to get things right.