The CPI has been gamed into uselessness because governments and corporations have indexed things like pension increases to it. The "hedonic substitution" concept is particularly disingenuous. Seniors can't afford steak any more and buy hot dogs instead? Inflation's gone down, yay!
The problem with US CPI is that the nation isn’t moving in the same direction as a whole, with some places and populations making gains far greater than others. It’s impossible to capture this one metric.
It isn't perfect - arguably there is no such thing as a perfect way of capturing the differences between changes in what's available and what's expected over time with respect to things like CRT vs LCD monitors - but portion sizes are relatively simple for adjustment