It's definitely a cockerel but the breed is a little strange. I too thought it doesn't look as round bodied as cornish crosses usually do, but maybe it is still young. Also you haven't been intentionally feeding it as much as possible to make it grow faster like some do.
Its a shame you got the wrong breed because yes these types of chickens tend to not live very long, but they can live happy lives with some special care.
As for him hurting your pullets, only time will tell how aggressive and frequent he is with mating. I've personally seen roosters mate hens half their size and weight without issue but they were very gentle roosters.
Also pullets and hens can and do crow sometimes, but it is quite rare and I believe it is caused by hormonal imbalance and/or ovary dysfunction. But your chicken's comb and wattles are too large at that age to be anything other than male.