I think you are absolutely right. Also when compare side by side, the Serbian version is the longest.
The Serbian language reform of the 19th century resulted in distancing from the literary standard (the so-called slavenno-serbski), a mixture of vernacular, Russian and Curch Slavonic, used in administration, schools, and generally by educated middle class, and redefining the "standard" according to the vernacular.
It's like dumping Queen's English and replacing it with cockney (and then stripping cockeny of all Latin and French words and replacing them with words from some other language)!
Typically, the more grammatically primitve the langue is the more words it requires to express itself. Thus, very ancient languages such as the Basque dialect in northern Spain, requires inrodinate number of words for a simple sentence in English.
I just find it interesting that Serbian is (predictably) the longest version of the three precisely because it lost (in addition to a rich Slavonic vocabulary) the gramamtical complexity (and expressive ability) through the reform.
Actually, the verison of Serbian still used by the Church for homilies and the Bible is the Synodal version of the NT, which uses the aorist, a grammatical form no longer used in the day-to-day vernacular. Without the aorist, the snetences beocme even longer.
Hereis an example to help you understand what I am trying to say: in English one can say "The Sitting Bull." In Russian, that would be "Сидящий Бык," but in Serbian one would say "Бик који седи" (the bull who is sitting). Sure, one can still say "седећи бик" (or in Russ. orthograpahy "седетьи бик") but it is "awkward." Such redundancy is typical of more primitive language forms.
I don't see how the sitting bull example illustrates the point you announce about primitive languages. I would not argue the point, -- it is logical that when a synthetic form, such as participle formation, is not there, one would construct phraseological solutions. Latin gives us examples of it. "Agenda" for example means "things that will have to be done"; any shortening of it in English ("to do list") would be idiomatic rather than precise.
Another example is in Horace (book 3 ode 6):
Damnosa quid non inminuit dies?
aetas parentum, peior auis, tulit
nos nequiores, mox daturos
progeniem uitiosiorem.
("What does not wasting time change! The age of our parents, worse than that of our grandsires, has brought us forth more impious still, and we shall produce a more vicious progeny.")
Here the bolded participle packs an entire phrase in English, "them, who will produce".
But in Serbian, the present participle is available; it is just something most speakers choose not to use.