Alternative term/phrase to 'Rule of thumb'?

I like using the term 'rule of thumb'. e.g., "As a rule of thumb it takes 10,000 hrs of practice to master a skill"

However it has come to my attention that it it may have a less than favorable origin

Therefore I would like to use a different phrase to indicate the same thing.

So what would be an an alternative term/phrase to 'Rule of thumb'?

You can omit the reference to the thumb and simply shorten it to

As a rule it takes 10,000 hours of practice to master a skill.

It isn't really a rule, but an idiom as given in Lexico

as a rule
PHRASE

Usually, but not always.

My suggestion is possibly too short and simple to be an ‘answer’ at all. A rule of thumb is nothing more than a rough guide.

There are well known ‘rules of thumb. In addition to the measurement of portions of rice, are many other forms of approximation: converting between various measures, including between imperial and metric, or celsius and fahrenheit. These can be called rough guides.

There are, indeed ‘general rules’, already mentioned, but these are rather different. Those are generalisations about things that are often or usually but not always true. This distinction is is a useful one, worth retaining.

Rule of Thumb :

A practical and approximate way of doing or measuring something:

A good rule of thumb is that a portion of rice is two handfuls.

Cambridge

I would suggest using the word 'approximation', instead.

A good approximation is that a portion of rice is two handfuls.

Approximation :

a guess of a number that is not exact but that is close:

Cambridge

The original saying was exactly that, an approximation of the diameter.