I agree with you completely about average people who aren't in a good cash position, but if we strip that all back and presume that the imaginary person is in a good financial position with adequate savings, no immediate goals (within 5 years) and who has a fund hundred £'s to spare each month - I still find it incredibly hard to argue against investing into a SIPP right now.
You can guarantee a 20% ROI immediately (obviously more if you're a higher-rate taxpayer). There is no alternative to someone who has spare cash they want to invest that would offer as good a deal as that.
Anyone who's fairly uninformed on the matter shouldn't be trying to time the market. They should set and forget, reinvest dividends, etc. And I will die on this hill.... no matter how qualified someone is, or how much data they've analyzed, no one.... whether it's Warren Buffet or Joe Bloggs, knows what's going to happen. The market could double in the next year. It could half.
This link isn't for you (as you obviously know a lot more on this subject than most) but for other forum members, read this article about
Bob, the world's worst market timer. It highlights quite well the fact that crashes are part of investing and if you're in it for the long haul you'd do very well to lose out.