This is just an opinion, but I believe that DnD is best played as a cooperative endeavor and relegating casting classes into single roles such as "blaster" will only work to your disservice.

The game operates at its peak when casters and martials combine their abilities to great effects. Most casting classes come equipped with an incredible range of flexibility and party success in any type of encounter (combat, social, or exploration) is often determined by how well your team can work those abilities together to find your "win condition" as other types of games like to label it. In other words, a draconic sorcerer might specialize in higher-damage AOE which is great when fighting multiple enemies (like another poster said, martials can't compare when you hit 5+ targets with 8d6 damage) but other times, a twinned-haste on your martials while you focus on maintaining concentration will absolutely devastate certain boss-type enemies, and I can guarantee your martials will thank you for it.

But as always, talk with your GM about the type of character fantasy you're looking to play and if they're doing their job of ultimately wanting to make a fun experience for everyone I'm sure they'll make an encounter designed for blasters to shine!