There is overwhelming evidence that sanskrit, greek, latin etc. are cognate languages and that they had all descended from a common ancestral language called proto-indo-european or PIE. It is quite possible that PIE originated in India (something western linguists reject). Hardly any scholar (even Indian ones) would claim that sanskrit is PIE. An important word like "surya" is the result of sound-changes from an earlier word in PIE - perhaps "swelyos" (to account for greek helios, latin solis and so forth.)
If Vedas are apaurusheya and eternal - how can it be justified that they are in sanskrit (and even the sanskrit of hindu scriptures can be seen to be changing between earlier and later books of rig veda and between vedas, upanishads, epics and puranas) and not a more pristine language?