Assume a learner wants speak Japanese fluently in 2 - 4 years and is not super concerned about developing an accent. The learner has currently been doing input only for one year. The learner decides to replace some of the input time with an output-feedback loop (e.g. speaking with a professional teacher with feedback). Will this necessarily be less efficient? What percentage of input time would need to be replaced by an output feedback-loop before it would be counter-productive? This seems like an issue of opportunity costs and marginal utility.
For example, I’ve heard many people recommend to only meet with a tutor to practice speaking 1-2 times a week. Is this because efficiency decreases after that? Assume I have infinite money and have no problem meeting with a tutor to practice speaking 5 times a week instead of practicing input with that same time. Would it be wasteful in terms of opportunity costs?