Yeah my impression is if there's a third deck that can "outvalue" (read: go into the late-game without automatically losing) against the Field of the Dead decks, it's Fires - mainly because they have a ton of sweepers to stall the board, planeswalkers that can keep up in value, and Cavalier of Gales to fly over for lethal (can be pumped by the red Cavalier too).
Are you playing BO1 or BO3, Yondar?
EDIT: I feel like we're at the point where the Golos decks start running cards for the mirror in the maindeck. Cards like Agent of Treachery for example is a pretty reasonable card against most of the field, and it's amazing in the mirror, so why not play some. It's also awfully hard to rush down the ramp deck. They can quite consistently start generating zombies by turns 5-6. Unless your creatures have some way to avoid getting chumped, you are going to lose eventually. I'm also thinking it's time to play Time Wipe instead of Realm-Cloaked Giant - the no-Giant clause is significant against certain cards, and the big difference (against control decks) is barely a problem since the zombies will grind out control no problem.
Some cards that I've run into that have been very effective against Golos:
Agent of TreacheryQuesting BeastVivien, Arkbow Ranger - reusable trample source. It's kind of hard for them to attack Vivien away.
Yorvo, Lord of Garenbrig - it can be chumped but in combination with Vivien it's given me trouble: it gets really big really quickly. This is why I'm thinking of running Time Wipe as the sweeper.
Other cards:
Ethereal Absolution - Two of these actually destroy the deck, even one copy should be very effective. The problem, of course, is that they're going to be sideboarding in enchantment hate once they see it, and if neither of you draw the sideboard card they're still going to win. Hell, they could draw their sideboard card and you not draw Absolution (i.e. they have dead card in hand), and they'll probably win anyway.
Legion's End - Based on theory this should be good, but it's only going to enable one attack; I've never seen the Golos deck run out of gas.
Casualties of War - okay, but who can cast this before they start making zombies?