I think a lot of the discussion about whether or not the feat tax business is necessary is getting away from the heart of the matter. Of course the PCs can do without them or by taking the feats as normal. Plenty of them do. While there is a discrepancy in PC vs. Monster attack vs. defense between the epic and the heroic tier, the question is which method of dealing with it is the most fun for the group.
Many people, advocates of fixing the feat taxes, want to reduce this discrepancy without impacting the other choices they have in character creation. This is nice, because it doesn't demand that PCs, and especially the party, be optimized. Players can make whatever they want, a suboptimal or optimal PC, and not feel like six of their feat choices are tied into some sort of arms race with the DM. They can spend those feat choices on something that ties into their idea of what their character is. The upside is the above freedom in PC design and faster encounters in the epic tier. The downside, is that when the party decides to bring the full resources of an epic tier character (buffs, resilience...) to bear on your encounter, you may find they have the ability to break it wide open. DMs may find they have to adjust. My group is casual, they want to have fun playing what they want how they want, so it makes sense for us. As a DM, I find I have to increase encounter difficulty at higher levels through increased damage, more monsters, or dangerous terrain and scenarios to counter it. It works well for us because we want a more cinematic and heroic feel to the game, and my players hate to spend a turn missing. I suspect that is why so many people prefer this fix as well.
Another option is to adjust the monster math behind the screen. This is a nice solution because only one person has to do the adjusting. It can be problematic for the same reasons as above. PCs, especially optimized ones will be able to blow through the occasionally encounter. It has the added advantage of subtlety, but the disadvantage of not being tailored to each PCs weaknesses. When and how a PC needs to adjust to the math discrepancy varies by build and race. Doing everything behind the scenes without player input can help or hinder certain builds differently. This is why I also advocate free choice feats instead of specific bonuses or feats at certain levels.
Some groups are really into optimization and are good at it. These groups can make a party that can counter the discrepancy through sheer skill and tactics. For them the game is about pushing the boundaries of PC design, bending the rules of the game to their whims, and exploiting carefully crafted team tactics to ruin a GM's day. These groups will be able to the choices built into the rules to keep up with monster statistics and not see any real difference in their combat effectiveness or the length of combats. The upsides are little GM adjustment and increased game challenge which many people really enjoy, the downside is it demands skilled players and that a PC's combat effectiveness and ability to work with the team take precedence over making a PC that fits your theme. Some player's will find this too constraining.
Last you can just play it as is, ignoring the discrepancy, making a character as you see fit, and relying on an epic tier PC's incredibly resilience to survive in the long run. Encounters will be long and drawn out grins, but the party will still likely survive. The upside to this, is that fights in the epic tier really do feel epic and almost hopeless. The PCs will feel outmatched, will miss often, and will watch helplessly as their FRW defenses are autohit or the GM occasionally takes a lone PC out to the woodshed and beats them down, laughing at their ineffectual attacks which must hit on a 15 or higher. But after the long and drawn out battle, the PCs (dead or not) will get up, dust themselves off, and enjoy the feeling of accomplishment gained from defeating a god on their own terms, with a PC designed exactly like they wanted. It has the benefits of an old school, grittier, and patient style of play. PCs will feel like Gods and Demons are a special challenge outside of their normal reach; something which must be prepared for instead of simply one of their four encounters a day. It has the downside of requiring mature and patient players who enjoy this style of play. It can be hard to find an entire group comprised of such.
You can counter the discrepancy using any one of or even a mix of the above. Pick your poison. If your group doesn't have fun with it, pick a different one. The game will always be about having fun with your friends and not how you decide to play it.
tl;dr There is a discrepancy in PC & Monster attack vs. defense between the epic and heroic tier. There are numerous ways to handle it. Pick the one that you think your group would enjoy the most.