both 2e and 3e flaws where pointed out to me. Once I saw it, I could not unsee it. 4e I found them mostly on my own. I don't even agree with everyone online (I still don't think expertise was that bad in 4e, and really don't see power attack even with leap attack and a 2 handed weapon in 3.5)
In my experience you can totally even run into the flaw without seeing it.
Example: I watched and said nothing as a group with a half dragon fighter, a half celestial (half god fluff) paladin, Drow half dragon wizard/cleric and half elf Monk.... I loved that they thought the Monk was Over powered and never realized that he was 5 or 6 levels above everyone else because of ECL... but even they saw a problem when the paladin died (glorious and honorable death) and the player brought in a human wizard/loremaster and boom came in "lower level" and still had so much more power.
I think possibly that the biggest issue is levels played. I've been in several groups where the highest level character is around 10th level. They just don't play higher than that. Which, in 3e, hides most of the major issues. Nobody bitches about a 4th level wizard, really. Yes, you can break the game in single digit levels, but, by and large, you have to know what you're doing to do it. For those who don't really care, it's not going to come up.
Where I really got an eye opener is when I started playing (well DMing) double digit level games. Wow, that's where you see the issue, if it comes up, which isn't guaranteed. I remember the group had a halfilng paladin for the longest time, and no problem at all. Actually seriously underpowered to be honest (the player had multi classed to monk and then pious templar). The character was virtually unkillable, but, couldn't hurt anything. When the character did actually die (nothing is unkillable

) the player brought back a straight human cleric. The campaign by this time was 15th level or so.
Now that was a shock. The player went from being more or less invisible in combat with the paladin, to completely dominating every encounter. So, to answer the OP, yes, I did see the problems I complain about in play. But, I do agree that for a lot of groups and for a lot of time, the balance issues that people kvetch about are largely unseen in play.