It is clear that when Pakistan top batsmen did not do well their middle order batsmen stepped up. This shows they have strong team that can adjust. They scored 201 runs for 7 in their 20 overs without pressure from other team. With this steady pace even after tough start is key sign of good T20 batting.
Bangladesh however had opposite problem when they lost wicket their scoring speed really slowed down. This means they do not play aggressively like T20 games required. Your point that Bangladesh batted like ODI and Pakistan played like T20 style explains this difference. In T20 cricket it is vital to keep runs coming and hit boundaries mostly and it sounds like Pakistan did this well while Bangladesh struggled.
Saim Ayub is making a come back in international cricket after recovering from an injury, may be in next few games he will regain his form. Both Pakistani openers failed in first T20I but good thing is middle order batting gave a good support that helped Pakistan in setting a target of 201. Hassan Nawaz is a good discovery for Pakistan, if he keep performing like that he can be a valuable asset for Pakistan team who is desperately in need of batsmen that can perfom.
Bangladesh still has two more games to make a comeback and Pakistan must not take Bangladesh light as they have the tendency to win both next games.