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"Balancing portfolios is basically a universally recommended practice."

The 'balancing' is against a stock market index which will seriously over-represent a particular geography, industry sector, business size, asset class etc. Why choose that index? Because the stock market tells us to?

"If you manage your own portfolio,"

I was considering how to make a 'passive' index fund even more passive.

"won't you have a similar "churn rate" to the index fund?"

An index fund would have a higher churn rate and therefore higher costs than my theoretical fund, but I do not know how much money an index fund spends on index-following sell-buy transactions.