This is true. If Monero adopted Drivechains I think it could become a real contender. Still, though, it would have to migrate most of its activity to the sidechain and make mainchain very small, in that sense it would be basically the same as eCash, only with a bigger initial user base and name recognition. The bigger question to me is: can Monero scale to billions of people via Thunder-style sidechains but with Monero technology? If yes then those sidechains should probably be used in eCash instead, but I don't know.