I'm not skeptical at all — I think it's very promising. And thanks for sharing the link to the lit review. They're a little more cautious than you, but do think the research trends are very promising (and I agree; we're really not disagreeing here, except on the level of confidence which we apply to a causal link):

"the clinical studies included in this review have yielded conflicting results. Some authors have found no correlation between engaging in physical exercise and the risk of tumor progression. Specifically, two RCTs failed to demonstrate a link between PA and PSA kinetics. However, after observing the participants of the Prostate Cancer Lifestyle Trial for two years, it was noted that the rate of definitive treatment was significantly lower among active men compared to the control group (5% vs. 27%, p = 0.005). "

… and …

"To accurately assess the impact of exercise on the risk of PCa progression in patients managed with AS, further randomized clinical trials with extended follow-up periods, incorporating the use of wearable devices for daily PA measurement, are warranted."

In other words, it looks like we're onto something here, so let's tighten up the methodologies and keep pushing ahead. If I were betting, I'd bet that the evidence will keep accumulating until they decide to make physical activity a core part of cancer treatment rather than a secondary recommendation.