the problem, as i see it, was that handheld guns were pretty useless only a powered turret had any real chance of tracking a fighter,
so replacing the front turret on the halifax went on to try and get the halifax upto lanc performance and then you do it to the Lanc so dropping the halifax back again, plus it would have meant a delay in lanc production something harris would have fought (halifax and stirling he would consider but nothing should delay lancs)
harris wanted shorts and handley Page to crease production and retool for lanc
given the loss rates on the these two compaired to the lanc and you can see his point