Weatherless is definitely viable. You just need solid answers to weather teams. Like others have mentioned, Kingdra can wreck most offensive Rain teams once Ferrothorn goes down. Other common Pokemon like Rotom-W and Latios/Latias are great for facing Rain teams as well.
I find offensive Sun teams most difficult for weatherless teams to handle because most Chlorophyll sweepers can outspeed every common Scarfer. Weatherless teams commonly use Heatran to combat Sun teams but they often carry Dugtrio for that very reason. Thus, strong priority users like Dragonite are handy here especially since it can't be trapped by Dugtrio.