In some cases Zeroes definitely dropped their tanks, as in early war operations when the tanks were seen on the ground by the Allies. In the early missions of Tainan Air Group from Rabaul to Guadalcanal they apparently didn't, not sure why, shortage? USN F6F's sometimes didn't drop their tanks in air combat either, in that case it was limited supply of them on a carrier.I think that I have read that it was even worse for the IJN in that the Zeros had to (or chose to) retain their drop tanks for combat over Guadalcanal.
On range it's true the Zeroes were flying at very long range on the early missions to Guadalcanal, from Vunakanau field at Rabaul almost 650 statue miles one way to Henderson Field. However later on they were flying from, or could divert to, Buin, around 345 statue miles, far for most 1942 fighters but not for a Zero (Model 32's, aka 'Hamps', could only reach Henderson from Buin, not from Rabaul). And some combats between F4F's and Zeroes were between carrier based ones, a few Japanese carrier strikes on Guadalcanal, or F4F's escorting attack a/c against Japanese convoys well north of Guadalcanal, yet the results didn't seem to change dramatically.
And mainly, we're compared the results of Zero v F4F in 1942 to performance of other Allied fighters facing Zeroes in the same period. In many of those other cases the Zeroes were also flying from far away, as Formosa to Philippines, northern DEI to Java, Timor to Darwin: 500+ mile one way missions where Zeroes were more successful against other Allied types than against F4F's.
Also the other side of coin of campaigns were the Zero and Allied bases were close was that in latter case the Allied fighters could apply direct pressure against the Zero bases, destroying a/c on the ground and possibly catching them taking off: the RAAF and USAAF P-40/P-39 units in New Guinea in '42 operating from Port Moresby against Zeroes based at Lae, within their short range, were able to do this on occasion.
Joe