Unfortunately, I'm afraid you're right. Control's takeover of Leland sure LOOKED a heck of a lot like Borg assimilation, especially as it was shown in _First Contact_. I feel like this move is similar to what they did with the origin of the Cybermen in Peter Capaldi's last season of Doctor Who.
cheers,
Gabe
Speaking of Doctor Who...I believe a case could be made that it was actually that show that pioneered the idea of assimilation through nanoprobes (at least for televised sci-fi), back in the mid-1960s. The story "The Moonbase" (from the Second Doctor's first season) featured a moonbase (duh) whose crew was struck by a mystery illness that caused dark veins to break out all over their bodies before apparently killing them. The "dead" crew members were then later seen re-animated zombie-style under control of the Cybermen, their veined bodies now augmented with technological add-ons, still able to perform technical tasks but with no free will of their own. Sound familiar? Although not called "nanoprobes" (I think they called it a "neurotopic virus"--was nanotech even a concept at the time?), the clear implication was that the infectious agent somehow facilitated Cyber-control.
And then TNG came along 20+ years later and introduced the Borg, who were Cybermen taken to the ultimate degree. Doctor Who itself seemed to forget about this angle where the Cybermen were concerned, only re-introducing it with the Eleventh and Twelfth Doctors (particularly the latter), opening it to criticism that they were just imitating the Borg--when in fact they had been there first!
cheers,
Gabe