Darkblast and coffin purge are just bad cards for these type of decks since the combo is far more fast than any deck playing goblin welder (this guy is never a big probem) and same against stax. The fact is that it does not kill the only boringcrea that you could see on the table : meddling mage and true believer.
I don't know what are the card you wan't to remove with your coffin purge?
Why run kobolds where you could play shield sphere and phyrexian walker? the walls are really usefull against any kind of aggro-control decks, they are artefact for the blue part (if you run it).
Against meddling the
best card you can find is Massacre, free cost and it cleans up your opponent board and you keep your little wall that will give you again some turns before going.
Defense grid, i don't like this card since you have nothing to play it on turn one (you do not run moxen). You will then have to play it on turn two which means a turn three kill. The best card is xantid because it has a lot of synergy with the other piece of the combo.
Why would you play Death Wish over Grim Tutor?
possibly because of budget concerns.
I think you must not think a list in budget terms. First, write it with the best components you can find, second adapt it to the card you'll be able to play. I think we cannot deck-build in suboptimal choices.
I agree you can play without moxen and lotus because they are expensive and hard to find for just a tournament ( even if it's possible, i played about 20 tournaments being full powered (nearly each power was different) where i don't have even a mana drain.)