He did shoulder the responsibility of being professional during his stint as a captain despite unjust criticism aimed at him all the time. Now that he has resigned from the position he doesnt have the same burden of responsibility so he can let out a bit of steam.
The hidden agenda bit is not without any foundation either. Yahya Hussaini, Mirza Iqbal Baig and the panel on Geo have always been using ugly tactics against him and have openly lobbied for his removal both on the media and in private. This is Pakistan cricket after all and ugly politics is a part & parcel of daily life. Players have groups and now these groups have their supporters in the media.
The debate on being aggressive and defensive is a long one and we will have to delve into stats for that but Imran played with guys who are now known as all-time great legends while how many can you pick to have the same stature from 2011 onwards that have been part of Misbahs team?
Whenever I have given stats on what kind of imbeciles Misbah has been playing with the answer is "well he is andhon mein kaa*na raja...why are you comparing with useless Pakistani batsmen". Well atleast have the common courtesy to acknowledge that the kaa*na who has brought us this far werna saray he andhay hotay tu phir say Ireland say haar jatay.