Agreed!
I'm on 1347/1400 achievements and 1347 is 96% (14580/~15250 points, so I have ~95% if calculated on points).
There are 162 World Event achievements, which is more than 10% of the total, so you're going to need at least ~130 of theses to get to 98% of the total achievements, which I guess in theory could be done in ~10 months, but this would be that you'd have to be pretty much on 100% of the non World Event achievements.
So I'd say ~10 months is theoretically the shortest time possible to get 98% of the achievements done, depending on which of the WE's you're going to do without / when you start the race to gather the points.