Relative to Bitcoin, yes, that's correct. Just depends if rate of adoption surpasses technological limits/consumer tech. If it doesn't grow too fast it shouldn't be a problem.

FCMP++ (an upgrade coming to Monero in about a year) will allow layers on Monero. An encrypted basechain with a privacy layer is about as scalable and private as you can get for crypto. 

 By the way, Bitcoin can also become expensive to run with massive usage. All things equal, Monero just reaches that hypothetical state quicker. But there is a scenario where Bitcoin can have massive adoption and be expensive to run, while Monero with modest adoption, remains less expensive. Just depends how the future plays out.