yeah the advantage that i think shrieker have over dragons is their adaptability. against certain decks you can have leave them unburrowed (especially in l3) however you also have the option to burrow them if your are fighting a deck that could potentially have rain of fire. otyughs aren't a real big problem for me (i use 18 stone pillar, 6 graboid, 6 shrieker. so a typical time/earth deck) because they can only eat one and you can play 2-3 at a time to get 'em past. its all about strategy. the problem with dragons is that as long as your opponent has no creature control hey do more damage, but almost all t50/pvp decks have creature control. with shriekers, if you have 6 burrowed shriekers thats 24 damage, after 2 turns they will be down to 52 hp (assuming that you haven't already some damage, andlets face it chances are that if you have 6 burrowed shriekers you prbably already have done some damage.) at this point point you can unburrow your shrieker to do 48 more damage, leaving them with 4 hp, which almost any rare weapon will take care of.
another thing with my deck is that if my opponent plays sundials i will simply hold on to shriekers in my hand and burrow any that i have on the field and not evolve graboids, this means that even under the cover of sundail my opponent can't do much to me (except build up quantums for a fire/ice bolt/life drain rush) but then when the sundials come down i have a damage potential of 56-64