Fangraphs has a good explanation on their site. And yes, it's been discussed here many times.By ESPN's WAR calculation (they use b-ref's WAR formula, I think), Betts is still ahead of Bogaerts, despite what seems like Bogaerts having a much better season at a premier position so far.
Betts: 13 hr, .268/.388/.458/.847, 3.3 bWAR
Bogaerts: 17 hr, .295/.385/.535/.920, 2.7 bWAR
But then Fangraphs has it different:
Betts: 2.6 fWAR
Bogaerts: 3.7 fWAR
Which seems to be more accurate. How does b-ref calculate WAR different than Fangraphs? I'm sure that's been asked here before but it seems like those are quite disparate numbers.