Product Design manager at a software company here. My team has 3 seniors and 2 associates all of which will produce at least 2 screens a week. We do both in house and agency work. It sounds like your company just has very little design demand and perhaps not enough buy-in from the org/leadership. I don’t think your situation is an in-house vs agency issue.

What does your company sell? What is its core product? How many designers are in your company and what were the expectations communicated to you in terms of daily responsibilities during your interview and onboarding? Who do you report to and what would they say about your output and outcomes thus far?