That's obviously correct, but it seems weird to use a different metric for market share and lock-in. If you define Google's customers as ad buyers, then they're very much not a monopoly, have way less than 91% market share, and their competitiors don't have a lack of users.
If they have a monopoly on search because of their share of searches, then surely the relevant lock-in would be how easily users of search can move to competitors?
