200 Watch - ETAs for GMS

I am averaging ~250m EXP per day(except during the weekends), yet it only says I am averaging ~100m EXP.

You're disregarding 4 days from your average.

Of course the results of 5b/14 are going to be lower than 5b/10.

What you can get on the days you train isn't indicative by itself of your results unless you train every day.

If I were to, for example, get 500m XP tomorrow because I spend 16 hours on 4x, that doesn't mean I'm going to hit 1b the next day unless I do it again.

That's why you used an established period of history to determine trends/averages.