Also regarding the point about new clients... wouldn't you face the same issues with a hedge fund also though? Say you have a new client that comes in at the market peak. In a HF structure, they'd still be buying the fund at an all time NAV high (which is essentially the same thing as slicing the new client account at current prices to match the model portfolio wgts in a SMA structure).
I agree onboarding new clients at market peaks is definitely not optimal. But I always figured it's the clients decision when they'd like to fund, and only the PM's responsibility what to do with assets afterwards. To Mephitopheles' point, if you think prices are too high to purchase for new clients, why not sell the stake for existing clients as well? If you're using new client's inflows in a HF structure to bring down your equity weighting, you could achieve the same goal by selling securities for all investors in a SMA structure. The only difference is that in the HF structure you use new inflows to "dilute" the equity wgt, while in the SMA you have to actively sell (and suffer tax implications). Let me know if this makes sense... I'm don't know if there are other tax implications also.