As a language learner (working on my 8th right now), I dabble in Duolingo from time to time and agree that it provides contact time with the language, and any contact time helps reinforce memory.
Language learning in general though, I have found, is not that amenable to gamification. Some learning methods may be more efficient than others, but even with the most efficient methods, real language learning is still inherently and unavoidably a slog. So if you come across a method that makes it "easy", chances are it's not actually working. It's too easy to trick oneself to think that one is making progress, and then find oneself unable to communicate when called upon to do so.
In the polyglot (ie actual practitioners of extreme language learning) community, there are many super talented language learners but a common pattern among them is the use of surprising traditional learning methods. Most do not use Duolingo but instead elect to do things the hard way, by actually going through workbooks, talking to tutors on iTalki, making mistakes, exposing themselves to media, translating, etc. Space repetition tools are sometimes used. Pimsleur is good for speaking, but not reading/writing so it doesn't get used that much.
There are clips of YouTubers where creators show you how to learned a language to a conversational level in 24 hours etc. but if you look more closely, the experiments are highly edited and the actual outcome is not that great.
I've resigned myself to the fact that the way to actually to learn a language is to jump in and do it the hard way, rather than through easier shortcuts. Language learning is about creating new reflexes and creating new pathways int he brain and there's no easy way to do that (the brain itself resists) without discomfort.
That said, tools like Duolingo do create fun and interest in a language -- and fun is needed to sustain oneself through the journey.