2 Megapacks, 1 Rare Players Pack, 30k coins and qualificiation. For those of us who aren't great players the rewards are decent but I question if they are worth the time in the weekend.
For example Squad Battle Elite 1 is easier to achieve and only demands 28 games over the weekend, 17 during the week but with the spacing being better the rewards are pretty much a match for gold 3. 2 Megapacks and just shy of 40k coins. Way less stress involved too.
Of course WE league comes with monthly rewards SB doesn't which is the real difference with 3 guaranteed inform players if you make gold 3.