LOL I did say the companion was card advantage but however it was meant for EDH. Trying to implement some form of commander play into other formats didn't bold well. Other players still can't interact with companion until it hits your hand which of course you pay 3. Then you still get priority with known information that everyone knows about. So in essence it is a pay 3 generic mana tutor for a specific card and in this case it is the companion and at sorcery speed which is only done in main phases. I don't see this as a bad thing it just makes strategizing a little more interesting
At some point you're right. But I'm looking at this mess from a different point of view:
EDH is already kinda restricted because of the nature of the format. The big card pool makes somewhat up for this, but you're still restricted. If you want to use a companion, you'll have to restrict your available card pool even more, in order to pay for the card advantage (the only non-restriction companion has become banned before the set was printed).
And now, after some people have already aranged with this and build their decks, the cmc for the extra card (which they already paid for with additional restrictions) doubles. EDH is a little slower than the other formats, especially at the kitchen table. But turning cmc 3 cards into cmc 6 without any compensations makes a huge difference.
In my Kelsien deck I added Zidra because she allows me to put some equipments on kelsien cheaper. Since zidra "only" lowers costs up to 1 mana, her usage is sometimes already restricted, since this lower limit doesn't allow her to use the full reduction potential on all equipments. and now I have to save up 6 mana in stead of 3 before she get's removed just to get out with +/-0 mana wise.
This difference in addition to the limitation zidra brings in order to play her as companion really makes me think about rebuilding the deck again and just use zidra as a 99er, ignoring the new (and interesting) mechanic. I'm really not sure she's worth the limitations anymore. This would also allow me (again) to add cards like
Puresteel Paladin or
Auriok Steelshaper which also work fine for the purpose and doesn't have this lower limit.