The real problem inside of the aikido world is the lack of real understanding. Everyone wants to focus on the "fine details" and the subtle uses of energy or technique. The problem is that grossly almost no one seems to understand the system.

Aikido like all martial arts is not flawless, and it's techniques are not without the weakness. But when someone says they "ask uke to add resistance" what are they asking uke to do? If you can't understand what Aikido is teaching you, then how can you "test" it?
For example, if I didn't think that MMA techniques worked, and I'm new to MMA (that is to say I'm not a regular competitor in MMA). How could I test it's techniques within the confines of a dead form? Aikido techniques and the majority of its practices don't use alive training methods, so all you have to "test" is a dead form, a form that you don't understand. If you want to test it outside of a form, and I don't really know the system, this too would fail, and be a bad test.

If you are working on some technique, within a dead form, uke must understand what it is that the form is working towards. For example if it's Ikyo, then uke must give up the elbow and relax the shoulder for that technique to be successful. If by adding resistance you mean that you are asking uke to push his elbow down and tighten his shoulder then Ikyo will never work- that is not what the technique is designed to do. It's like practicing a dead form for the jab, and telling your sparring partner to resist you by defending the jab, and then getting upset because all of your jabs "fail". Within the confines of your dead form you can't make something work when you set it up to fail.

Get a living practice, it's not your arts fault, but your inability to understand what it is that your art is doing. That coupled with a dead practice equals the frustration we see in many of those who practice Aikido.