Bracha Achrona on 7 minim

On 35a, the gemarah attempts to learn out the choyuv of brachos from the 7 minim, whose bracha achrona is doraisa (i.e. learn out the bracha rishona of 7 minim from the bracha achrona with a kv"ch, then extend to all foods with a binyan av). Ultimately the ability to learn from 7 minim is rejected ("sh'chayn chayavim b'bikurim"), but the noti0n of their bracha achrona being mi'dioraisa is never challenged.

On 44a, the mishna quotes R' Gamliel as holding you bentch on the 7 minim, but the chachamim disagree and say may-ayn shalosh. The gemara explains the chachamim's position that "eretz hifsik"; the posuk of v'achalta
v'savata u'varachta only goes back on the prior words of "eretz asher lo b'miskaynus tochal ba *lechem*", not the pasuk before of the 7 minim. It seems clear according to the chachamim that the bracha achronah on the 7 minim is *not* from the torah! This conclusion is expressed by Rabeinu Yonah (44a) and the Rambam (hilchos Brachos 8: 12). Is our gemara on 35a only going according to R' Gamliel?

Years ago someone showed me the following idea (in shut minchas baruch, siman 5), which provides an alternative approach. The Tur writes in orach chaim 209 that if you have a safek about whether you've said al-hamichya you must repeat it, since it's a chiyuv *dioraisa*! How could this be, if the chachamim on 44a reject the connection between the 7 minim and the pasuk "v'achalta v'savata u'vayrachta"? The prisha suggests - though the chiyuv on 7 minim doesn't come from the pasuk in eikev, there must be some other (hidden) drasha, or halacha l'moshe misinai. The minchas baruch doesn't like the idea of making up new mystrerious drashos, and proves from rishonim that they associated the 7 minim with the pasuk in Reah. He suggests that the chachamim on 44a *don't disagree* that the pasuk refers to shivas haminim as well. The point that "eretz hifsik" means only that there is a distinction between 7 minim and bread, and they don't SHARE the same bracha achrona; bread gets bentching, 7 minim get may-ain shalosh - but both can be dioraisa.