This is not true. A well built team weatherless team can handle just fine opposing rain and sand teams. Sun teams are usually problematic for weatherless team but every team type has weaknesses. Stall is very weak to heavy offense, and sun offense is weak to sand teams with Hippo. I think your problem is that a good weatherless team is harder to build than a weather team, but this shouldn't be an issue. Some team types were always more difficult to team build with and to use, but this doesn''t make them any less viable, and is a poor reason to argue that something is broken. For example weatherless teams with Celebi have little troubles with rain teams, except from a few specific Pokemon such as Tornadus, NP Thundurus-T and SD Toxicroak (after an SD boost obviously).