yeah i know that his voice should be like super awsome so that's maybe why they didn't added it so it doesn't disappoint the watchers if the voice is not up to their expectations,but let's face it... i liked his voice in the anime but it was far away from perfect,i think they could have found someone with a decent singing voice here....
when he sang to maho and at Dybre it was ok that they hid it it was building up the tension and the effects were nice , it would have been ok if he would have sing just at GGGS5 i think
but do you think there is a chance of BECK:MCS season 2 after this ? it would be badass