On this, I would say no. In fact these session will be a really good marker for your aerobic base, by monitoring how much your HR “drifts” in the second hour. That’s when the good work is being done, when you need to keep pushing out that steady power as your muscles slowly fatigue.
As for the Zwift races, are you sure it isn’t a case of power to weight? Is it partly that other riders actually need to push out less power to get up the climbs?
Secondly, is 305 your ramp test FTP? If so then your actual FTP (i.e. the power you can hold for sustained efforts) is moderately likely to be lower. And in which case that 290 watts is closer to threshold than you think - so no wonder you don’t have much left in the tank when they hammer it over the climb.
So overall I wouldn’t overthink it. General Build is a good program and I don’t think there’s a change in emphasis that’s going to radically alter your performance in these races.