You are making false equivalences all over the place. This isnt Bush I or Clinton, this is a GOP party that has no identity outside of being on the wrong side of most social issues (compared to the majority) and using old Reagan economic policies to placate their corporate masters. They dont support science, they have no jobs plan, they want wars all over the place and dont want to fund them. Some of the candidates are full on fundies, some are tea party nimrods and some are full on wackos that only seem to care about the upper crust of this nation. Even the so called "true believers" like Rand tuck tail and run cause they know they have zero chance in the primaries if they arent bowing to the military and praising Jesus Christ and his First Knight Sir Ronald Reagan of Nazareth! The Libertarian Wing has been neutered because the fundies and the Koch's just have too much cash.
If this was a 3 person race you would be absolutely correct, you dont need to unite the bases you just have to convince enough of them to shift the tide. When 12 guys are running, and their platforms are a scatterplot of random GOP ideals ranging from moderate to lunatic across the board, you need a guy who can walk in and get everyone to say "that is our guy". Right now not one of these guys can do that even your precious Walker. Sure he talks the talk but he will buckle to public pressure just like the rest and his record is pathet-a-sad.
They wont put the true believer up though because they will go down like the Titanic. (as you pointed out with the Minnesota GOP) They can raise money talking about abortion, gay marriage and ObamaCare all they want to but fact is they got nothing to replace it and honestly they cant say we are worse off now than when Bush left office...not with a straight face anyways. (and I say this as no big backer of Obama for quite some time) You put a guy like Walker up who parallels Dubya in policy and who destroyed WI like Dubya destroyed America and you are looking at a laugher. Jeb may be dragged down by name but Walker will be destroyed by his actual record.
IMHO this is what the GOP needs, they need to get trounced and have the leadership implode. If that is why you ant Wlker to run then I change my tune and support you 100%