It isn't so bulky (HP is decent but defenses are not) which isn't complemented by a pretty crappy typing in normal leaving it with no resistances meaning it isn't really an ideal switch in on incoming attacks. It also lacks a lot of speed. If fully invested, it hits a speed stat of 258 which is fairly underwhelming and also makes it very easy to revenge kill. Investing in speed is essential however to out speed some threats. This means there is no room for potential HP investment.
Exploud is one of them Pokemon that will be viable in the higher tiers however it has little going for it outside of Boomburst meaning there are better options available. There are simply bulkier and faster wall breakers avalible. Many hit harder also. One of Exploud's many critisims is its inability to deal heavy damage against opponents with its other coverage moves. It just doesn't have the SATK to hit awfully hard when not using Boom Burst. Its speed stat and normal typing hinder it and keep it in RU bound.