I know that this might sound as a blasphemy, but it doesn't make much sense splitting Slavic verbs along the "perfective" and "imperfective" line. This opposition is simply not built into the Slavic verb system.
This understanding of the verb aspect in Slavic languages is put forward in Comrie's work on the verb aspect:
Students of Russian and other Slavonic languages are familiar with
the distinction between Perfective and Imperfective aspect, as in on
pročital (Pfv.) and on čital (Ipfv.), both translatable into English
as 'he read', although some idea of the difference can be given by
translating the Imperfective as ' he was reading, he used to read '.
Speaking for Serbian (and I strongly suspect the same applies to Russian) Comrie's understanding of the contrast between "čital" and "pročital" must be erroneous on many levels. In the first place, understanding of "čital" as a strictly imperfective verb is untenable. We cannot possibly know whether "čital" receives perfective or imperfective reading without the context, simply because such opposition is not built into the language. What adding the morpheme "pro" to "čital" does is it changes an atelic verb into a telic one. Slavic (or at least Serbian) verbs contrast in terms of their telicity, but not in terms of perfectivity.
Similarly to Comrie, the authors of the Cambridge Grammar of the English Language say this:
With perfective aspectuality, the situation is presented in its
totality, as a complete whole; it is viewed, as it were, from the
outside, without reference to any internal temporal structure or
segmentation. The concept of complete whole is independent of time, so
that perfective aspectuality is compatible with any time-sphere: past
in He declared it a fake, present in I declare this meeting open,
future in It is essential [that he declare everything he’s bought].
With imperfective aspectuality, the situation is not presented in its
totality; it is viewed from within, with focus on some feature of the
internal temporal structure or on some subinterval of time within the
whole. In languages such as Russian there are distinct verb-forms
whose basic meanings correspond closely to these two aspectualities,
and these languages are therefore said to have perfective and
imperfective aspect. English, of course, is not such a language: the
simple present and preterite can both be used either perfectively or
I'd say it is on the contrary actually, the perfective / imperfective opposition is pretty much grammaticalized in English considering that in English we can clearly align "perfective" aspect with all (single) event verbs and imperfective (progressive) with the (be +) ing verb form.