Not obeying Waver doesn't make him less impressive. It doesn't make him more impressive either. Any Servant wouldn't respect him. He's just a wuss, full of himself and confident of his own abilities, before he got into the War. Now he shows, or is at least discovering, how outclassed he might be.
What disappointed me is that he's just a noble idiot thus far. You have a point that he may be faking it, and that certainly is a possibility given his earlier displays of robbing libraries and watching tons of videos and declaring Bill Clinton as someone he'd have to worry about. Where he failed was underestimating the pride of both Saber and Lancer. Granted, there isn't much of a way to know how much Saber (possibly above all other Servants) wants the Grail. Seeking it was a major one of her life goals. In his heyday, he commanded a great deal of respect, and brought a huge number of warriors into his armies, as he conquered them. But here he is fighting heroes and Kings. So few of them would ever bow to the authority of another besides their Masters.
It was like Rider was ignoring everything he should have learned from the Grail. The Grail imparts knowledge of both the War, its rules, and the modern era. Yet Alexander chose to study on his own as well, and apparently ignored what the Grail would have told him about the relationship of Servants and Masters. He was appealing to other Servants warrior to warrior, something he could understand. He should have been appealing to their Masters.
He's got a lot of pride and confidence. That's great. But he isn't showing much subtlety or insight, yet. Confidence and pride without insight brings hubris. Hubris in a War like this leads to one's undoing.
Rider's own words in episode 12 of the FSN anime: "Curse yourself as much as you can, for you are not even able to touch this creature." Rider truly believed that Saber would not be able to touch her once she was on her Pegasus. Both from its aerial maneuverability and its speed, especially with Bellerophon. Excalibur moves in a straight line. Even while she was charging, if it truly was slower, Rider should have been able to dodge it.