It becomes a problem when the players aren't having fun.
Most things do.
I'm glad that works for your players. It doesn't for mine. Those who've figured out the system synergies feel punished if I try to reduce their effective solely because other players can't find those same efficiencies. And any help offered to those who made less-effective characters caused bad feelings with them.
I've often observed players helping each other out; after all, someone who wants his character to be effective generally has a vested interest in improving the effectiveness of his comrades. I've also houseruled a lot; less to fix specific issues that arose during play and more to fix conceptual problems that I had with the game or to tweak it for my own preferences.
I have observed situations where players didn't like being told that their abilities were not going to be as useful as the rules said they would be.
For example, another psion player learned a power that granted him +30 to Int-based checks, and asserted that I should provide a comprehensive and accurate answer to any knowledge question he asked, because the highest DC for Knowledge checks is 30. I understood his interpretation of the rules, but I did not think it appropriate that his character be literally omniscient, so I gave him some information that wouldn't otherwise have been accessible, but often said no when he asked extremely specific or plot-breaking questions. He wasn't happy, and no one else was really happy with him. He never backed down, and neither did I. That's an example of a broken mechanic that really needs to be rewritten, and also a player who really needed to be more reasonable.
So yes, said problems exist, and yes, interventional solutions are not always optimal. I don't think, however, that every psion power needed to be exactly equal in utility, merely that the ones that allowed the player to do to much needed to be fixed.
Yes. I think you and I are more centrist on this topic than either of our posts make us seem.
Great!
Certainly. It should never be the only aspect given attention, but it should be kept in mind. I think 3E started off well, but as new options emerged it was if the designers of those new options forgot how customizable the base design was made.
And before anyone chimes in with the advice to just not use those new options, I will restate one of the joys of playing this game that my group shares. That is adding new options as the game goes on. If we can't do that without the game breaking (for us), then it's not a game I want to play.
"Power creep" is definitely a legitimate issue.
As I've stated above, I think balance becomes a less appropriate discussion when you're talking about disparate concepts. If you're talking about comparable concepts, it becomes more important and more actionable. For example, if Jump allowed one to duplicate the meaningful effects of Tumble, it would be overpowered, because there would be no point in taking Tumble. "Skills that let you move athletically" need to have one paradigm and need to work with each other. However, I don't think it would be reasonable to try to create and equivalence between Tumble and Diplomacy or Knowledge (Arcana), because they are completely different concepts.
Similarly, I think it's rather important that a barbarian and a fighter be balanced closely with each other, but how they compare with a bard is something that is harder to articulate and less important to manage.
At no point am I trying to say that balance is not a real thing, merely that it isn't the most important of all things.