See, here's the problem with concentrating on one aspect of a character for a while, people get the often-mistakened impression that this one argument is the primary point, and without it the entire argument fails.
No, not in the slightest.
The issues brought up with ICs in successfully fighting peach are as follows:
1. They're young kids, even without her being physically fit, they're still early enough in their development that she has the advantage.
2. Mountain-climbing interfered with their normal growth, so they have muscular degeneration and are actually weaker then normal kids their age.
3. Their CANON weaponry is ineffective.
4. Peach has bombs that act like grenades.
5. They are 3 times the width of peach, therefore they have morbid obesity.
One of those arguments was disproved, namely that she had bombs that act like grenades. Of course, they're still effective, just less so.
That still leaves arguments 1-3 and 5 that you have no response to.
Arguments that Peach would lose are as follows:
1. There's two of them.
Response: They're still less effective then Peach for the above reasons, even together.
2. They're more physically fit then her.
Response: They're morbidly obease as shown by their proportions, and kids their age are simply not capable of competing with the raw strength of a grown women, it's too early in their development. Also, there's the issue of muscular degeneration.
3. Their weapons are better.
Response: Their better weapons are non-canonical.
In other words there are an enormous number of issues you need to contend, the fact that her bombs are not as useful as originally thought in this match-up shifts it very little.