Imperial measurements were based on arbitrary things, metric has specific scientific definitions for their weights.

What do you mean? A pound is legally defined as 0.45359237 kilograms.

And the kilogram is defined:

The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6.62607015×10^−34 when expressed in the unit J⋅s, which is equal to kg⋅m^2 ⋅s^−1, where the metre and the second are defined in terms of c and ΔνCs.

These are all currently defined off of the same universal constants, just with different multipliers, which are all arbitrary numbers: 6.62607015 is just about as arbitrary as 0.45359237. Hell, the number 10 is arbitrary, too, so we still use a system for time based on dividing the Earth’s day into 24 and 60.

Like, I get that there’s some elegance in the historical water-based definitions derived from the arbitrary definition of length, but the definition of “meter” started from about as arbitrary a definition as “foot” (and the meter was generally more difficult to derive in the time of its adoption based on the Earth’s dimensions).