As you saw, carbon rims are very stiff and therefore do not deflect at the contact point. Instead the spokes give and the whole wheel deflects. This is a different behavior from a trad wheel. The slight downside is that, going hard out of the saddle and rocking the bike, there will be some rear wheel deflection which can cause unexpected tire rub. Not easy to predict. Try it and see. I have friends who do long stretches of gravel on carbon bikes with 25s.
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