Bracha Rishona - d'rabanon or d'oraysa?

We always assume that brachos rishonos are d'rabonnon but from the gemara in Brachos on daf 35a it really sounds like brachos are d'oraysa. First of all, the gemara quotes a pasuk (Tosafos answers this by saying that the pasuk is just d'rabonon). Second of all, the gemara has a kal v'chomer which stands at the end of the gemara at least for the 7 minim (you could answer this by the pircha the gemara used on daf 21a that she'kein nehene). Finally, the gemara concludes that we say brachos rishonos because of a svara. The Pnei Yehoshua proves from this that brachos Rishonos are d'oraysa. A svara always works on a d'oraysa level as evidenced from numerous gemaras that say "lama li kra, svara hi" or "iy bayis aima kra, iy bayis aima svara."

He addresses a couple of questions that you might have like safek brachos l'hakel and the gemara we had earlier that said that a bal keri makes brachos acharonos but not brachos rishonos seems to imply (as Rashi explains) that it's because brachos rishonos are d'rabonon.

From our gemara it certainly appears that the Pnei Yehoshua is right. My only problem is that none of the Rishonim say this. I guess that they'd have to explain our gemara that there are svaros d'oraysa and svaros d'rabonon. I'm not sure how to distinguish to determine which ones are which and why they all assume that this svara only creates a chiyuv d'rabonon. I guess that they just feel that the pashtus of the other sugyos is that it's d'rabonon so that must be all this gemara means also.