I do think part of the problem with Dallas was the lack of strong women, they were just there supporting the male leads, eg JR, Bobby, and Cliff (and Jock at the start). We never really saw a big strong female character, by the end of the original run all of the female leads were gone (Miss Ellie, Pam, Donna, Sue Ellen and Lucy). Cliff's mother was promising, yet they killed her off not long after they introduced her - she would have been a great lead but she wasn't the "Alexis" figure you suggested.
Of course had they gone down that round then it would have been seen as "Dallas copying Dynasty copying Dallas" but I do think it needed a stronger woman - no offence to Linda Gray who I adore but really all Sue Ellen did was to react to JR's affairs, get drunk, have an affair, get back with JR and start all over.
I don't know if a true Alexis character would have worked, but I feel that if they did have a really strong woman in there they ought to have kept her around, rather than 1-2 series there to support a man or to give JR someone to fight with. I suppose we came close to it with Leanne De La Vega, but yet again once she had sold Ewing Oil to Michelle for the price of a bag of chips, she was off again. What a shame.
There was also Marilee Stone who I absolutely adored, she was beautiful and witty, and had a strong appetite for the birds and the bees, but again she was there only to make JR look good. She performed that role incredibly well, creating that character was an act of real genius, but she would not have been the Alexis figure.
I have said it before but they could have done so much with April and Michelle had they thought about it properly. I would certainly not have killed off April (I know she was pregnant) but she was a real fine actress/character and there were so many layers to her.