Moving to a new investment based on projected return/standard deviation

Do you think that moving from an existing money manager to a new one in a taxable account based on projected return/standard deviation for the next 1, 3, and 5 years is a reasonable basis? The projection also includes confidence intervals for the projected returns. All projections are based on modern portfolio theory. The projections come from the risk and return characterisitcs and their correlations with each other over the previous 10 years. If no data is avaliable for the security or ETF a benchmark is used. For example, if there is a healthcare stock that has only been around for 4 years it would use 4 years of the stock and 6 years of the healthcare sector index. This is something I’ve encountered in the real world and was wondering what you thought