The belief that Russian mercenaries in the Donbass would be eventually relieved by conventional forces has been around since then, yes. Many were surprised by the fact that it was not happening, year after year. At some point the consensus in policy circles was that Putin must had decided to keep the area as a wild-west buffer.

The recent deployment near the border wasn't the first, although it was definitely an order of magnitude bigger - there were, in fact, questions on whether the exaggerated scale was so brazen and disproportionate (and unbalanced - their Asian border is now pretty weak...) that it couldn't be anything more than posturing.