Of course Arjuna had his ego as all the others. He was not a saint trying to merge in God. It is just that the Pandavas, in general had more of a Rajo-sattwic ego whereas the Kauravas, in general, had a Rajo-tamasic or strong Rajasic ego. Feeling emotions and attachment towards brothers and family is part of the Sattwic ego.
As to Sri Krishna using him as an instrument, that is a different matter. The Divine can and does use anyone as His instrument. Napolean and Churchil were both instruments of the Divine but both had serious defects of Rajasic nature. The Divine uses men as they are depending upon their readiness and openness to the Divine Force and its workings. But it will be a mistake to think that Sri Krishna couldn’t have managed without Arjuna. He himself declares in the Gita that He has already slain them and Arjuna has just been given the privilege of being an instrument since he is dear to him through lives. In fact Sri Krishna was alone was quite capable of destroying the entire Kuru army as he did demonstrate when he defended Arjuna with a wheel against Bhisma. But Arjuna had to be given his chance and everybody had to play their role and make their choices.
Affectionately,
Alok Da
