This is the kind of brilliant observation that shines a kind of light over the landscape of music history. Yes, the basic characteristic of Baroque music is its sweeping continuity. Here is an example from Bach:
That is all about spinning out the basic idea through a kaleidoscope of harmonies and sequences while avoiding big cadences except at major structural divisions because, for the Baroque, a full cadence tends to bring the music to a halt.
The transition to Classical style was all about developing, as Rosen says, the short, articulated phrase and the articulation was primarily through cadence. In other words, while the phrase was given shape and structure through melodic and rhythmic devices, the most important structural foundation was the harmony, meaning, the cadence.
Looking at the two basic kinds of Classical phrase, the period and the sentence, we can see how this works. The sentence has two parts: the presentation and the continuation. In the presentation, which is typically 4 measures, there is a 2 measure basic idea (statement) which is repeated (response). The continuation has another 2 measures in which the basic idea is fragmented with harmonic acceleration and ends with another 2 measures of cadential material where the basic idea is liquidated. This ends with either a half cadence or a perfect authentic cadence. In the period, also typically 8 measures, the antecedent part has a two measure basic idea followed by a two measure contrasting idea and ends with a half cadence. The consequent part repeats the 2 measure basic idea and then the 2 measure contrasting idea, but ends with a perfect authentic cadence.
The beginning of Beethoven's Piano Sonata in F minor, op 2 no 1, is the perfect example of the sentence:
That first phrase, a sentence, takes up the first 15 seconds of the clip. The second movement of Mozart's Eine kleine Nachtmusik gives us a good example of the period:
The first phrase, a period, takes the first 23 seconds of that clip.
The relevance of this to the composer now is that in our long journey away from the classical style through romanticism, modernism and post-modernism, we have somehow, quite inadvertently, managed to work ourselves back into that "encompassing and sweeping continuity" without those crisp articulations of the Classical style. Just look how popular drones and minimalism have been.
Now I know that composers have all sorts of amazingly complex ways of structuring their music. I have come up with a couple myself. But from the listener's point of view the effect of a lot of 20th century music is that of continuity and by that I mean that, despite an often spiky and jagged surface, the listener does not hear crisp phrases articulated clearly. So, in a sense, we have returned to a pre-classical kind of texture. Let me find an example or two. Here is Dérive 2 by Pierre Boulez. However the music is structured internally, what we hear, I think, is a kind of continuity without articulated phrases:
And even when we look at the post-modernist music of Steve Reich and Philip Glass, even though there is the return to tonality, there are no cadences to articulate phrases, so the music again has a kind of continuity:
That was the opening of Music for 18 Musicians by Steve Reich and here is the first part of the Symphony No. 9 by Philip Glass:
The problem is how to direct the music, how to build excitement, how to hasten to a conclusion or close off a section. The continuity we can do, but the rest is difficult. I think composers direct the phrase (if there is one) and build excitement and close sections with a variety of means involving timbre, dynamics and rhythm. But we cannot use cadence for structure because we have lost the use of the cadence available to the Classical style and have developed nothing that quite replaces it.
Let's hear a little Haydn, one of the great masters of the Classical style and listen to how he articulates his phrases and builds his structure. Here is the Symphony No. 39 in G minor: