I'm certain that there is much truth in this idea. Russian singers still talk about the "Russian bel-canto school" here, and there is a traceable "family tree" of teacher-pupil relationships that illustrate the way the technique was passed down.
By coincidence I went to a concert two weeks ago to mark the 80th birthday of veteran Bolshoi Theatre bass Alexander Vedernikov, who sits very clearly in this tradition. Most of the concert was made-up of performances of his pupils (including the astonishing tenor Gurets/Hurets whom I mentioned in another thread), but Vedernikov himself sang a few numbers, including Dosifei's narration from KHOVANSCHINA, and the bel-canto technique is clearly evident.
Of course, in parallel with this there were alternative singing techniques, more related to the German style of production - and some others which were uniquely rooted in Russian traditions (for example Vishnevskaya, who never had a lesson in her life, and was rejected from her Bolshoi audition precisely because she didn't have the Russian bel-canto style). And there were also singers who made a career more from Party cronyism than any actual vocal prowess - but without the technique to sustain them on stage, these careers rarely lasted long.
The bel-canto school is still alive and well in Russia (and the former USSR countries whose top singers mostly came to Moscow or Leningrad/Petersburg to study with the best teachers), and can be heard today. Anna Netrebko is the most obvious example, but there are lots more: sopranos Tatiana Kuinji, Marina Andreeva, Ludmila Kaftaikina, Ludmila Shikhova, Marina Karpechenko, Marina Kalinina; mezzos Larissa Kostiuk, Ksenia Vyaznikova; tenors Alexander Gurets, Mikhail Gubsky, and the veteran lyrico-dramatico Zurab Sotkilava; basses Taras Shtonda, Mikhail Serov... and probably lots more
(NB this isn't supposed to be a list of famous Russian singers, but a list of those who sing with the bel-canto technique... I've excluded singers like Diadkova and Gogolevskaya, who are excellent, but sing with a different technique).