And we people have said in the past - dead does not mean out in this game. If you're just playing Guild, Dreamer, or one of the Masters who relies on heavy alpha strikes to get the job done, then generally yes you can cripple their force by removing models from it. Other Masters actually expand their options by losing models, as counters are much, much more usable in this game than in Warmachine (or 40k, but they barely even exist in 40k) due to the fact that they persist in the game world, and are not 'claim at generation or lose em'.
Claiming that dead models don't counterattack is focusing on an offensive way of thinking that assumes the best option is not to leave anything standing to oppose you. This doesn't always work - take a good summoner Master or a Lilith grow list and hitting the non-essential parts of the list (the stuff you'd need to engage first to reach the essential parts further in) means that you're giving your opponent an advantage in soul stones and resources.
Heck, look at Pandora, who is considered a powerhouse model. And this is mainly due to the fact that fighting Pandora is counter productive - you're more likely to have taken damage from than she is. Or wipe out all of Hoffman's crew but he and watch a bunch of your own vanish in a giant scrap explosion. Dreamer's real strength is not necessarily his alpha strike (which is good) but the fact that his mobility and place effects allow him to access the key parts of your opponent's crew who are behind their front line.