Am I wrong in assuming that Page was inserted into the organization specifically to develop the pretense that Trump should be surveilled?
I don't assume that, and for various reasons. But, that assumption might hold, too.
I think Trump was under surveillance before Carter Page and Papadopolous joined the campaign. The surveillance has NO pretext. It was done as a matter of seeking advantage where ever it could be found. At some point before Page and Papadopolous were identified, Trump's opposition chose "Russian collusion" as a viable false accusation. There are multiple reasons for this: Trump had conducted Miss Universe, sought deals in Russia; opposition wants to increase tension with Russia for geopolitical purposes.
I think Trump's campaign selected Page and Papadopolous, without them being pushed forward by team Obama, team Comey, or whatever label attaches to the opposing force.
I think Page and Papadopolous were targeted as capable of being "tainted" as "Russian links" - and this was AFTER the Russian collusion scheme" was hatched - by review of list of names that team Trump submitted to WaPo as foreign advisers. See "Byron York: When did Trump-Russia probe begin?."