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without potentially wasting a winter of training?
No training is wasted. It'll have some effect and at the end of it you'll know if that training was a good idea or not.
Also, everyone changes. You might respond well to one thing one year and do that again and you get no benefit.
You couldn't even claim that any training method was 'bad' (unless it directly results in injury or illness I guess) because you don't know that some kind of different training for that year wouldn't have provided a worse result - you might think you were shit because of your training but maybe your mind/body was just doing something else that year.
I guess what’s optimal is different for everyone. But the question is how do you find out, without potentially wasting a winter of training?
Polarised training makes sense, take the traditional winter base riding but add some high intensity to stay sharp. Particularly if you don’t have full time pro rider hours available.