Due to my career, I've had the opportunity to travel to various Aikido Dojo across the United States. I've visited Aikikai (my "style"), Yoshinkan, Ki Society, Iwama; just about every major variant of Aikido (except for Tomiki). I admit, I've seen some Dojo that do not use what I would consider to be a committed attack when training. At my dojo, we focus on a committed attack; meaning that if the Uke does not redirect the attack or at the very least move out of the way, the Uke will get hit. Will the Uke get knocked out? No. The reason being is that there is a difference between having a committed attack and an attack that is meant to cause harm. Control is important when studying Aikido; control in attacking, control in defending, controlling the Uke, etc.
OK, about the blocking. I've always been taught and continue to teach that there are no "true" blocks in Aikido. Karate uses blocks which stop the strike or kick, not necessarily redirect it. Aikido (at least not in any dojo I've visited) does not employ blocks that stop the attack, but uses techniques to redirect the incoming strike or kick. This method of defense makes Aikido more fluid. It has always been my opinion that if the person attacking is stronger than you, it's much easier to redirect the attack than it is to try and stop it with a block.
Of course, I could be wrong. But then, it has always been easier for me to redirect my brother's senseless grabs and punches (good natured fun really) than it was to try and block them.
Perhaps the dojo you have started training at does not have the same philosophy as mine. Jim, you said that the punches / blocks you have seen are weak. Please don't think that this is true for all Aikido dojo. Like I said, and Matt as well, different dojo train in different manners.