Weather-boosted vs. super effective moves...

the ideal is to use a tool like poke battler and find out what are your best mon for a specific boss with your fighting style and have a prepared party for your raid. However, reality is not ideal, and in the end the size of your group is a bigger factor than if you take the ideal party. Unless you are trying to raid with a minimum or close to minimum group it's probably more convenient to just go with the recommended even if they may not technically be your most efficient squad. Also be aware that the ideal party for some bosses is move specific and you won't know the raid boss' moves until you've jumped into the raid.

Weather is a 20% boost. Super effective is a 40% boost. STAB is a 20% boost. Type effectiveness provides the larger boost. Some Pokemon, however, are strong enough to bridge the difference between weather boost and super effective.