The prayer of me’ein sheva does NOT include any mention of making the wind blow and the rain descend, which is me’akev (in the 2nd bracha). So how can one be yotza if he is missing an essential part of SE?
If one forgot to say mashiv haruach on Friday night, and he listened to the chazzan with intent to be yotzi, does he need to daven Maariv again? (The same question can be asked regarding Fri night Chol Hamoed, that there is no mention of the festival.)
Good point. Because of this reason there are opinions that on Friday Night if someone forgot to say mashiv haruach he may still be yotza bedieved by saying along ( or listening to) magen avos with the chazan. However this is will only apply to mashiv harahon Firday night.
Regarding Yaaleh V’yavo there are opinions that according to this he should be yotze, however this is not the consensus of the poskim.
O”CH 268-13,M:B 28, Biur Halacha 114 D”H Machzirin Oso, Maharsham Siman 268-13, R’ S. Z. Brought in Siach Halacha siman 114 that Yaaleh Vyovo is different, and we can’t learn it from what R’A Eiger says because it is only an addition to the SE and it isn’t an integral part of it, therefore there is no proof that because it wasn’t included in the bracha that he still is yotza. See B”H 268 -13. Also see Kol Hatorah 67- pg 25.