Bungie seem to have left an oversight in Destiny 2: Beyond Light that lets people farm up to 1,200 power in a matter of an hour or two by just farming a Lost Sector.
Widow's Walk Lost Sector in the EDZ can be found by spawning next to the church and entering the damaged building to the left of it. Proceed in a straight line until you find the steps downstairs and then just follow the tunnels until you see the image from above, informing you you've entered Widow's Walk.
Make sure you bring the best loadout for bringing down bosses since that all you'll be doing. Jump over all those Fallen, head straight for the Wanted boss and burst him down. The boss drops almost gear with an almost guaranteed significant upgrade in your power level. Leave the Lost Sector by running out and once again ignoring all those other Fallen. As soon as you are notified you reached Trostland, turn around and enter Widow's Walk again. That's all there is to it. Rinse and repeat.
A few suggestions for the ideal farming loadout would be to bring a Lightweight kinetic weapon, The Fourth Horseman if you have it in special slot and pretty much any sword in the heavy slot.
As for the abilities, it's suggested for Hunters to go with the middle solar tree and Shards of Galanor Exotic which will let them use the super on every run. Warlocks can bring Geomag Stabilizers with Chaos Reach while
Titans are probably best off with Thundercrash. They may not have the super up as often but anti-boss weapons can make short work of the second rate villain in a Lost Sector.
Bungie will probably nerf this way of levelling soon so make sure you farm up as soon as you see this.