Yes.
Pali is practically synonymous with the Pali canon. It has had no independent existence outside of the Pali canon and its derivative literature. Since the earliest times, it has not been used by anyone except Theravada monks, and they too have been using it only under the firm mistaken belief that it was the Buddha’s language. But the Buddha could have only used a language in which he was spoken to by the rest of his society - and not in a language peculiar to himself or to Buddhism, which necessarily therefore was not a Buddhist-only language like Pali.
So I don’t see with what logic/confidence Prof. Gombrich (and/or other scholars) would be able to claim that an exclusively-Buddhist language like Pali could have been the Buddha’s language.
Buddhist Hybrid Sanskrit (BHS) is not a Prakrit, but rather a form of Sanskrit restored from Gandhari texts. It is about 90% identical to standard-sanskrit, it shares its remaining 10% peculiarities with Gandhari & Pali. In my understanding, BHS represents the language of EBTs progressively restored from Gandhari to Sanskrit - and hence it contains many incorrectly sanskritized expressions (or hyper-sanskritisms, as they are called). Logically therefore it appears that those who were restoring from the Gandhari were not themselves sure what exact sense many of those words and expressions in the Gandhari EBTs made.
It is very likely that the Pali canon is also redacted from a Gandhari prototype (where the Gandhari manuscripts available were quite fragmentary (with words and phrases and even paragraphs missing here and there), which is how we usually find them today. This would explain why Pali suttas appear to have so many canned phrases (or ‘band-aid phrases’ as I like to call them) to make the suttas ‘whole’ again. It may have been a common technique also used by the BHS EBTs but nowhere does the use of the canned phrases appear more prominent than in the Pali Suttas. Outside of the EBTs, such canned phrases are virtually unknown in other Indic prose literature (including Vedic prose).
As far as we can see, most extant Gandhari texts are also mainly (though not exclusively) Buddhist (and its use was geographically limited to the Gandhara area), so again it is unlikely to have been the Buddha’s language.
As I said, BHS is for the most part Sanskrit itself (and its peculiarities stem mainly from the fact of its restoration from Gandhari), and therefore doesnt have much of an independent value.
That leaves us with late-Vedic, which, based on what I know, was a massive language spoken by nearly all Indo-Aryans in the Buddha’s time (and which in its 4th century BCE grammatically-standardized form is known as Classical Sanskrit) - and which was optionally spoken with svara intonations.
There remains the question - Why does Gandhari and Pali even exist in the first place if late-Vedic was spoken by almost all Indo-Aryans? It’s because (as I mentioned elsewhere):
- There were Achaemenid-era Iranic linguistic influences in India that gradually were causing phonetic and morphological confusions in late-Vedic. This must also have been the reason why the extremely thorough generative grammar of Panini had to be composed at this time specifically to validate grammatically correct usages.
- The introduction of writing in Aramaic script (which caused further phonemic confusions as the script was not designed for a phonetic representation of Late-Vedic Sanskrit) followed by marginally improved scripts like Kharoshthi and Brahmi which were still not capable of phonetic representation until they evolved sufficiently enough over the centuries and were fully suitable to write sanskrit phonetically accurately only by the beginning of the common era.