So I've been thinking through a landfall deck and, realistically, I see two ways to take it - hardcore aggro (likely the better route) or mid-range.
In the event you're going aggro, may I suggest the following build: https://deckbox.org/sets/1214820
You might be asking, how is this better than what you're running? Note that, outside of the singleton Omnath (who is in just in case the board stalls out and partially for grins), my curve stops at 3. This might not be correct, as Grove Rumbler certainly provides an appealing option at four. The idea here is to let you get a few things onto the board and then your land can be directed toward the pumps and tricks. Ideally on turn 4 you're swinging, pumping, and using Temur Battle Rage to end the game, rather than playing the rumbler.
As for your build, Break Through the Line, Subterranean Scout, and Retreat to Valakut are totally sub-optimal choices if you're just looking to get damage through. The idea of only making a single creature unblockable really is just lacking for an aggro strategy unless it's a major impact creature. Two options for you to consider are Magmatic Chasm or Firemantle Mage. The former will allow you to likely just swing free and clear. The latter gives everything menace and will likely ensure at least half of your team makes it through.
Honestly, on the topic of Atarka's Command, it's worth it if you have them, but without I don't know that it'll make or break the deck. I can see where your win percentage will drop a few points, but it's not like that one card makes the whole deck go, especially with the other options available.
If your intent is to look more mid-range, I can offer the following build: https://deckbox.org/sets/1214846
Admittedly, this one is a bit more cute, with an emphasis on elemental tribal. It could work, it might not, it's worth a shot.
I hope some of this makes sense and is of some use. If you have any questions about the thought process that motivated my card choices and I'm happy to explain.
Best luck!