I highly suspect companion drop RNG is heavily influenced by the player's active companion, and much as everything else in this game, RNG is purposely weighted counter to the companion's current gear. For instance, if the companion is kitted with a sword, board, and heavy armor, the chance of the drop being a heavy armor piece or one-handed weapon will be statistically lower than light or medium armor pieces.
Anecdotally, I can report that the foregoing is absolutely my experience since Blackwood launched. I've been playing a heavy armored Bastian and have had only a couple applicable drops -- I have many duplicates of light armor pieces, restoration staves, and infernal staves. (My Mirri is in medium armor and little medium armor has dropped either.)
What I'm getting at is RNG is highly rigged. Another example is dungeon drops, where a magicka player more often gets heavy or medium armor pieces and if weapons drop at all they're likely melee weapons or bows.
I'm down with RNG, but have no love for developers that fiddle with it to prolong the agony for no better reason than a greater chance of extracting real money from players the longer they play. I highly suspect that's what ZOS has done. It's a strategy very akin to outright extortion. Someone please prove me wrong.