This is a wrong-headed way of thinking about it in the early stage, IMHO, because it gets everyone into the mindset of I do x, and you _only_ do y, instead of the mindset of what I bring has no value by itself and what you bring has no value by itself but _together_ the knowledge, skills and hard work we bring are worth something.

It’s almost impossible to predict (or even tease apart afterwards) what things increased value and what did not. So forget about trying. Understand that ventures are risky, and focus on getting from zero value to something of value.

If you’re seriously concerned that your partner isn’t fully dedicated, an uneven equity split won’t fix that.