Outsider most certainly meant the loss of verb forms compared to OCS which is considerable.I have only some notions of Russian, acquired fifty years ago. Russian has perfective and imperfective verbs. This splitting does not exist in french, nor in latin. I think that imperfective past in russian is exactly imperfect in french, perfective past in russian is what we call "passé simple" (or "passé composé" when there is an auxiliary verb).
This moves me to wonder whether the conjugational systems of verbs generally are more resistant to dilution or simplification through mixture or contact with other languages than are nominal declensions, and if so why. The Romance languages, for example have all but completely eliminated the Latin-type declension of substantives (except in number and gender), while retaining complex conjugations for their verbs (in French this is particularly so in the written language, even when in speech the distinctions have been reduced or abandoned - "je fais", but "il fait"); and this applies too in German - even relatively recently one may observe the disappearance of the distinct dative form "[dem] Mann(e)", for example, though verbs remain systematically conjugated in most tenses and moods, and even (mutatis mutandis) in English.Originally Posted by Outsider
As were several Slavic languages, particularly in the Balkans, where Latin, Greek, and Celtic languages had previously been spoken.
Maybe that's why Bulgarian doesn't have cases and has complicated verbal system.