Yes. Learning ES5 means you'll miss out on some useful language features, you won't be able to use some of the more modern libraries in NPM, you'll find it much harder to carry on progressing once you finish the course, and employers are a bit less likely to hire you. It'd be like learning Python 1 or Java 8 now. You could make stuff, sure, but there are better ways now.
Thanks. The target audience here is beginners to programming or JS. I think learning ES5 isn’t a stumbling block, and it’s probably good as a basis to go on and learn ES6 features later. It’s more like learning the core features rather than an out of date version. I use typescript at work and I still use functions instead of lambdas, closures instead of classes where it makes sense for clarity.