That looks like a piece of box section steel subjected to the laws of physics if you ask me !
Yes you could brace the side rail more, but to what? Back to main chassis rail. With that sort of force something has to give, so wouldn’t an easily replaced side rail be better to bend rather than something further in?
Wow the comments from expert race car builders here. Possibly more Rees Built Cars out on the track these days than anything else ,so they must have something going for them. Pete and Ethan up there with the best of them as far as drivers go. That was an all in brawl as far as finals go and any car will bend if you put in the hits like those guys from both teams did, i have seen cars come out far worse off in the past .