Personally I use Flame Emp... I run Katrina and Blitz to hold them off for a few while building up my SP then eat them alive with flame emp and then fire dragon with 3 sylphs to up the speed of the fire dragon.
I normally have the affordability to sac the flame emp once or twice to deal 50 dmg again and again... assassin and merciless death ruin my day though.
the issue i had when i took him out was the fact that ther was ALREADY 4 cards of theirs on the field and i wasnt generating SP enough (even after letting 4 of my guys eat at my soul cards and 2 rapid growths) to keep my burns coming.
My generally strategy (that seems to work out well) is launch emp after initial little monsters beginning phase of the fight and spend my racked up sp on flame tornados and fire arrows.
The starts been my bread and butter except for when i face the best of the best who play these two types of decks.
dalos IS powerful but keep in mind his ability is very costly. most decks that i see him in are built around him (and maybe another big creature), he's not something you can just throw out randomly and hope to use well. a 3SP ability is something you're only going to be able to use about every other turn unless you have prepared ways to get more SP.
so, he is strong but there are other monster decks out there who can take him on in similar ways. plus the usual assassin or salamander soldier SS can mess up a strat like that.