OB1
Jedi Master
How do feats and MC make that much of a difference? I play a RAW campaign playing a published adventure and I see some of the "problems" noted in OP, but I have never played without feats or with MC, so I have no reference point. Feats dont seem to a high impact on our game.
They don't necessarily make a huge difference but they can. With Feats and MC turned on, if your group then goes for full optimization, there are synergies that allow you to get quite a bit above the baseline in terms of power. As with magic items, they can simply make you better than what the game was designed for. Combine that with white grid encounters and a misunderstanding of how CR and daily encounter math works, and combat can become trivial using the base single encounter guidelines.
Of course, your party chose abilities specifically to become more powerful than the baseline, so I can never understand why people then complain when that shows up in play ( [MENTION=12731]CapnZapp[/MENTION] for example, has issues with his game because of this, and then blames WoTC for not designing to his baseline rather than designing for the majority of players). It's like buying a Ferrari, driving it at 120 on the freeway and then being surprised when you are passing everyone else on the road.
There has to be a baseline somewhere, setting it for new and casual players makes sense, as it allows the game to be much more accessible to the masses. Hardcore players can either adjust that baseline to their tastes with the tools provided or turn off options to keep things in line.