Dies to Removal

No, I think KDL is fine in place of Confidant if you're looking to be really low curve aggro. If anything, maybe you don't need Flamespeaker and Confidant in the same deck.

I like KDL because he assumes ultimate form more quickly than FoD. Plus, you can get him there 1-2 mana at a time, leaving mana up for necessary removal, where FoD requires you to have 3 and 6 mana available all at once.

I'd prefer Figure or Kargan Dragonlord in place of Goblin Guide, personally, but haste is hard to argue.

Kargan is a human, and I know you want to go big. When he's good, he's very good.

The Dos Rakis concept was good because nearly every creature had haste, the synergy between humans and Falkenrath Aristocrat was amazing, and it could reliably sideboard into a bigger deck (4 Thundermaw Hellkite and a 25th land in for game 2) when needed. It also didn't have to fight combo, so tapping out was an attractive option.

In Modern, you're punished for tapping out by Twin, Pod and fringe combo like Ad Nauseam. Your threats should be cheap, and your removal cheaper.

The 4 Stormbreath Dragon are great if you're living to turn 5, but you really have to ensure that you pack sweepers, single target removal, and enough land to cast them on time.

If you just want to be an aggro deck with a big finisher, look to cap your curve at 4 so you can run less land and more removal.

My Dos Rakis concept -

[deck]Dos Rakis Modern[/deck]

I favor Slaughter Pact in this deck so you can tap out on T3 while providing protection against Twin / Pod combo.