Oh, no. Nationwide, McMullin had almost than twice as many write-in votes as Sanders. Many states did not even recognize Sanders as a write-in option (those states have laws or policies that they will only tally write-in votes for a candidate who had officially declared, with the top election official of the state, their intention to be a write-in candidate for President, which McMullin did in many states). Sanders had almost 112,000 write-in votes -- counted only in a few states which allowed all write-in votes to be tallied, even if the votes were for someone who was not an officially declared write-in candidate -- but McMullin had over 221,000 write-in votes, spread out across 23 states.
(Source: calculations derived from data from the Wikipedia page about Election 2016.)
However as you yourself stated many of Bernie's "official" write-in votes were not counted as opposed to McMullin, so although your statement is factually correct and accurate, it is much more likely that Sander's Write-In votes well exceeded McMullin's with Kasich running a far distant 3rd.
Unfortunately we will never know, but even in just a small state like Oregon that didn't count write-in votes by candidate at the statewide level, my estimate is that roughly 60-65% of Write-In ballots were for Bernie (And likely quite higher) vs 35-40% for McMullin/Romney/Obama/Mickey Mouse/Donald Duck, etc....
