As they say, 'Form is temporary but class is permanent'. Imrul is in good form but Tamim is pure class.
Tamim is a class batsmen and you guys are unduly worried about him. Even the best of the best batsmen will have few weaknesses and they find a way to nullify those.
Since Tamim is the number one batsman of the BD team, people do a lot more homework against him. If the opponents find a weakness they will utilize it to their best. Now Imrul has scored runs so SAfricans will do tons of analysis to find to his weakness as well.
Still not sure on Imrul but one knock from Tamim will start the turn around.