Ah yes, the good old days when Izuku was allowed to have introspection.
Anyways, there is a running theme in Izuku's thought process here. He didn't switch to legs because he prefers to fight that way necessarily. He wanted to maintain the use of his arms because of the importance Izuku puts on reaching out a helping hand to others. He was solely focused on being able to run towards those in need to be able to reach them.
And this internal narrative says a lot about Izuku's troubled headspace at this point. Izuku was blaming himself for All Might's retirement. He believed that if he had just focused on his legs earlier, he might have been able to run from Muscular and catch Bakugou to prevent Kamino.
Is this perspective in any way realistic? No. If Izuku hadn't stopped Muscular, there would have been likely multiple deaths in the hero course. And many members of the League's Vanguard Squad were present when they were about to leave with Bakugou. Even if Izuku had usable arms to catch the Baku-marble, there was a good chance the League wouldn't have accepted leaving empty-handed and a brawl would have broken out that might have ended in the same result or worse anyway. All for One would have continued to scheme against All Might and the embers of One for All would have eventually died out regardless of whether Kamino happened or not