I see plenty of stall and defensive teams, and I think this would be useful there. Good for wallbreaking as well of course, but stall teams could use it to force switches and cause even more passive damage because it applies to all damage, not just direct attacks.
The problem with making it so that indirect damage is boosted is that a lot of offensive teams also take advantage of those same sources of indirect damage.
Stealth Rock and Spikes are often set up by offensive teams to get that extra damage in and cripple foes to create easier sweeps, as well as stall teams that use things like Roar.
Poison and burn are used often to prevent the opposition from staying too long and forcing switches, as well as defensive teams that want to force switches to gain an upper defensive edge.
Sandstorm and hail damage are exploited by offensive teams that use those weather conditions, as well as more defensive-oriented teams that use those weathers to boost the survivability of their Rock- and Ice-type Pokémon.
I could see Sensory Beam affecting direct attacks, but not indirect ones, for that reason. Especially Stealth Rock. 60% HP damage for a Ho-Oh or 30% to a Lugia that's switching in is NOT fun. That 10% or 5% adds up fast.