Short answer - No. I was thinking about my nephews that are now in middle and high school. They both enjoy sports and I have noted the year-round approach that is so common today for youth athletics. There is no question that the jack of all trades is master of none does apply to sports, but what is the best way to approach the off season for a cyclist? Keep on training? Take a month off? 2 weeks? Try another sport? As with all things, it depends and I believe an individual approach is best.
I believe mental recovery and recharging is the most important step as an athlete heads into the off season. Preparing for a cycling season generally takes about 20 weeks and it is best to only start a structured progressive training plan when one is ready and motivated. This is different for each athlete in my experience. Some need some time away and some are ready to get started the day after their last race. I do not think there is a right or wrong as long as the athlete is mentally ready to start training when day 1 arrives.
A close second is physical recovery. Again, this is highly individual and many things should be considered, such as any nagging injuries, aches or pains that need a short break to resolve. The actual and training age of the athlete as well as the previous year's training load should also be considered. For example, a 20 year old that is training 15-20 hours a week is much more likely to benefit and need ~2-4 weeks off the bike than someone training 8 hours a week. Masters (40+) tend to lose fitness more quickly than younger athletes, so a longer recovery and detraining period may be advised against pending any injuries and motivation. If you tapered for a 50 minute criterium as your last race, then you are likely rested and not carrying much fatigue into the off season, so a physical recovery period might not be necessary. If your last race was a 7 day stage race with a big training block to prepare you, then some R and R is probably in order.
I do think some detraining is a good thing at times, but how much depends on the individual athlete - age, limiters, time to goal event, relative abilities compared to competitors and so on. A periodized training approach allows for letting some of the high end go and I believe this is necessary largely because the body will start to break down after several weeks of intense training. I would caution against too much detraining for Masters athletes as it takes a long time to get it back and I do not think it is a good idea to 'start over' each season. Why do that to yourself? It is okay and encouraged to go hard in the off season within reason.
Should you cross train with a different sport in the off season? Maybe. There is no question that cross training is good to balance out the body and a great thing to consider. But again, one needs to weigh out the costs and benefits of doing so. Will it delay or interfere with the start of training and leave you underprepared for your first 2018 event? Are you likely to get injured? Do you even want to cross train? If you live in California and your first race is in February and your last was in September there is not much time for other activities pending your cycling goals. If your first race is in the end of March then cross-training might make more sense.
Should you strength train? Yes, I think you should. I believe it will help with overall health - maintain muscle mass, strengthen connective tissues, help with overuse muscle imbalances, injury prevention and increase bone density. You will be able to train harder on the bike when that time comes. Will you gain weight? No, not really. There are athletes that put on muscle more easily than others, but it takes several of weeks of weight lifting to actually gain muscle mass. We get stronger quickly because our nervous system responds. I have seen a few athletes actually put on some muscle in a short 10 week program, but only athletes that had that muscle in the past and/or endurance training is cut back dramatically. Usually, the few pounds of weight gain is more from eating like one did when they were training on the bike and burning more calories than with strength training.
As with detraining - why shoot yourself in the foot by starting over every year? Change nothing and nothing changes. If shedding some unwanted body fat would be beneficial to your health and cycling goals then do it slowly and safely in the off season. This is a time that many cyclists gain weight and I feel it is a major mistake and one that I have made. The result was trying to drop this extra baggage leading into my target events and my training suffered. Bad idea - drop the weight now and gain an edge on the competition that is relaxing a bit too much.
These are my opinions. I think it is easy to find sources that will agree or disagree if one looks around and there are no absolutes when it comes to training and the human body. That is why I feel an individual approach is best and many things should be factored in when making decisions about the off season. I have seen sources that say athletes need 2 - 4 weeks completely off the bike and so on and I do not think those absolutes apply. I think the best approach is to look at your goal event(s), mental motivation, physical condition/injuries, current abilities and limiters, and time available to train. Then work backward from your event for planning out your off season. I would put a priority on the activities that give you the best odds for success in your event and get to work when your mind and body are ready. Listen to your body and think about why you are doing what to prepare yourself for a great 2018 season.