Perhaps they are. But then you get into the question of titling - if I call a two note phrase tapped out on a xylophone a symphony is it therefore really a symphony? OTOH, if I write something that is resolutely in traditional symphonic form but doggedly refuse to call it a symphony in any way, is it therefore not a symphony? The composer's intentions have to mean something - Mendelssohn called those pieces Overtures, and in fact, that is a perfectly good description of them - the overture as a form is perfectly legitimate. There is also the question of form and program - The Midsummer Night's Dream overture doesn't follow a program, it is a classically proportioned and structured piece whose themes are also representative of characters and locations in the drama, but which don't follow the drama in their layout. That isn't really the best description of a symphonic or tone poem to me*. OTOH, Fingal's Cave is much more like a truly progammatic work, more like a symphonic poem, though one of compact scale.
Re the Berlioz. Call the choral bits boring if you wish. But there is no way that those central orchestral movements - Romeo Alone, the Scene d'amour and the Scherzo - can be put anywhere other than amongst Berlioz's finest works. The Scene d'amour, in his own opinion, was the finest thing he ever wrote, and I agree. It is a ravishing, astonishing piece of music.
*And there is also that question of what difference there is, if any, between tone poem and symphonic poem...
