If one is unsure which blessing a food gets, you make the more inclusive blessing, defaulting to the most inclusive she'hakol if nothing else is inclusive enough to cover all of your bases (Shulchan Aruch in several places, example O.C. 204:13). This is called "safek berachos lehakel" (see Shulchan Aruch 168:13 glosses and many many many other places) which means we are lenient in blessings. Why is it called being lenient to make the more inclusive blessing? The implication is that were one to be stringent one would make the less inclusive blessing, even though it may not be the accurate blessing. Why would the "stringency" be to make the least inclusive blessing?
Additionally, several poskim (See Even Ha'Ozer about bean stalks in O.C. 204 and Ta"z O.C. 202:13) assume the "leniency" is in light of the prohibition to make a blessing in vain, not because of the requirement to make a correct blessing (i.e. were the blessing in vain not applicable, one would not apply the rule of "safek berachos lehakel" in order to insure fulfilling the requirement to make a blessing). Why do I not have an objective desire to make the most accurate blessing, and am willing to dispense of the surety of an accurate blessing in exchange for a more precise blessing which may not even be applicable to this food? I.e. you have a mystery fruit, could be ha'etz or adama, and you happen to have an apple. You make a ha'etz on the apple and do not make any blessing on the mystery fruit (that is basically the case of the Ta"z). Since there is no concern of an in vain blessing to make the less inclusive blessing, you do so and then don't worry about the possibility of not having made the correct blessing on the mystery fruit. Why am I not concerned for the accuracy of my blessing and what gives the other blessing preference?