Controllers aren't the only ones under pressure. We've had more airline captains recently start argueing with controllers at my facility than ever before in my career. I'm sure that they are being forced to 'do more with less' as we are.
Another explanation would be that pilots perceive a "decline in service" and complain because of that. You give all the arguments why service is declining.
What worries me is that there is no quick way out of the hole, even with excellent management it takes several years to achieve proper levels of qualified ATC; training takes time.