I don’t know if Compounding is the right term in this situation. Compounding refers to getting extra power from Feruchemy using allomancer, and I think it is somewhat specific to those two magic systems, with minor allowances for some situations (Hemalurgy, direct Shardic interference). I don’t think that you could gain EXTRA power from Stormlight, that just isn’t the way it works.
The term you should use is Resonance, because that is what would happen. Possession of more than two magics let’s you create new things. For example, there is Resonance between Dalinar and Shallan when they use their powers to create the map of the world. All Lightweavers have a Resonance between soulcasting and lightweaving, they gain the ability to take Memories. If I remember correctly, the Windrunner’s Resonance is reverse lashings (When they can attract objects to one another, not when they physically stick them together). Compounding is a form of Resonance, but it talks about a specific type of Resonance. When Wax creates his “steel bubble”, that is believes to be a unique resonance between his allomantic steel and feruchemical iron.
Possession of 2 or more honorblades is possible and it would create new combinations or Surges and new Resonances. The same would happen if you bonded with 2 or more spren of different orders, though Brandon has said that this would be very difficult to do. Another refutation of your argument for increased power, is the situation of bonding more than one spren of the same order. Bonding more than one spren doesn’t increase your power significantly or make your Stormlight usage more efficient.