This. I have a Tacx Neo and use Zwift and Trainer Road. I'll ride outside as much as possible but if it's slippery or too cold and windy for my taste I can get a better workout on the trainer. I have as much saddle time in the winter as I do in the summer.
Following a training plan on Trainer Road keeps it more interesting than slogging through a bunch of low intensity survival miles fighting the weather and I go into spring in better shape than a lot of my riding peeps.