Yeah that's a tough question to answer. While I agree that using age (100-age in PP) is too generic of a proxy, the general theme behind it is solid. If you were to do a standard stock and bond portfolio, what percentage in bonds would be right for you? That percentage in PP. The rest in whatever you feel most confident in. This can be a buy and hold allocation, or it could be some form of an active strategy. Either way, strategy diversification does help in the same way asset diversification helps.
These things are really individual though. It all really depends on individual need and goals. Need is something often overlooked. Someone with great need by definition needs to take more risk to hit their goals. Someone with moderate need really only needs a moderate portfolio (this could be 100% PP coast mode basically). However, an interesting switch happens at the top end of the spectrum. Where your need becomes low, and you're basically in (or on track for) "won the game" territory, the penalty to increasing risk goes down (especially so for younger people like me that can always choose to work longer if worse comes to worse).
I personally reached this point in the last year or so, where I surpassed my planned "won the game" track by a significant margin. Financially, I'm doing much better than I originally anticipated both in my career and in my investment performance, and I had to adjust my model accordingly. I reached a point where it became silly to not increase risk, because even with more risk and a historical string of bad luck, I would still hit my game plan goal early or on time of my original projections. So basically, I crossed into "why not?" territory. As such the amount that I keep in a conservative "diversified portfolio" has dropped from 60% of my portfolio at the start of the year down to 30% of my portfolio.
Now in the last year I've also adjusted the "VP" strategy to a quant strategy that I levered up just to the point of just less than a 30% max historical drawdown (you can see my recent VP section thread for more info). I chose 30% because a 40% future drawdown in that 70% of my portfolio is about the point that I would start to really get queasy, and I always assume the max drawdown of any strategy (PP included) lies in the future not the past. So in my case, since I'm not doing a buy and hold strategy in my VP, I didn't just look at need and goals, I also looked at what I was doing in my VP and how the two portfolios play together.
If I were looking at a VP strategy like buy and hold that would have a much higher assumed max drawdown, then I would have wanted to err on the side of less VP than more. So maybe that would have been going from 60PP/40VP to something more conservative like 50/50 vs my current 30/70. But when I backtest the whole of both PP an VP for my current setup, 30/70 is about the sweet spot of where I want to be risk wise. Hopefully me writing out my thought process in how I arrived at my breakdown might help you in your own process.