Re: big creatures.
Yeah, Malygos doesn't win the game the turn you play it, and protecting it and/or creating a situation where it will survive, like by baiting removal, is part of the strategy you use when you play it. My point is that doing something useful, and it doesn't have to even be as good as spell damage fan, it can be minor like an Emerald Drake rolling into your hand, something useful has to come out of a minion that costs 7+ mana.
I don't really think Ancient of War is a viable card. It wasn't in the Reginald list I copied for tournament play, and I didn't run into it all that much the month I made legend. Dying to removal is a serious issue for the card, and the only deck that Ancient of War does okay against is Zoo, but even Zoo variants with Power overwhelming can pseudo spot remove Ancient of War and beat you anyway.. but mostly the zoo variants aren't expecting it because they know Ancient of War is killing the rest of your matchup spread.
Sunwalker costs 1 less mana which is why it is barely viable. With a little bit of power creep and development in the game we might not consider Sunwalker a viable card anymore in the future.
Re: Ancestor's Call. I'm cautiously optimistic since Show and Tell is tournament playable in Magic, and that's a similar card. You choose what you get with that one, which is actually worse since an Ancestor's Call deck won't have cheap guys in it anyway, so only your opponent gets to benefit from picking and choosing.
Of course Magic doesn't have a hardcoded mana cap, so the cost of the available cards is limited by the developers' imaginations. And I think it took time for enough expensive dudes to exist for it to be good. But there's potential there. It might be something that takes a while to become good.
For Ancestor's Call to work you need a backup plan if you don't draw Ancestor's Call and that seems like the trickier part than "is cheating out a Malygos for four mana good enough". Alarm-o-bot is the only similar effect but Alarm-o-bot doesn't feel aggressively costed, 3 health is just not enough. Far Sight wants to help, but your deck will have cards that cost less than 3 mana so Far Sight will still suck. It looks like the best backup plan right now is spam spirit wolves and wait to hardcast but that might not be good enough, especially in a class with no ramp.
I'd be real excited if there's something else in the set to help out.