Alright then, let's say you're right. Say 10 million (the number of DDB users) is the current number. Granted, that's not all that solid either since someone could have made an account and then stopped playing, but, sure, let's use 10 million.
Now, again, FG is running about 100 000 tables. Roll 20 about the same number. So, at best, you're looking at 1 million gamers. Let's double that for everyone else. That still puts current VTT gamers at about 20%. Again, unless you think 90% of online gaming is being done by other programs and there's this massive group of silent people who game online but are impossible to count, my point still stands.
Note, also, that that 200 000 tables is of all games, not just D&D. The actual number of D&D tables is about 2/3rds of that (give or take).
Does it really matter if it's 5, 15 or 25%? FFS, the POINT is that online gaming is a fairly small niche of the total gaming community. WotC having a VTT is not really going to change that. It's simply a new market avenue, not a replacement for face to face gamers.