I am a senior getting ready to apply to PhD programs in Applied Physics (I currently am located in and plan to attend grad school in the US). I am currently working a co-op at a large company in a small, very research-oriented and very academic group doing research that is directly applicable to what I want to study in grad school. The group lead and another researcher (both hold PhDs) have agreed to write letters of recommendation for me, and the third will be from a professor at my university.
Today I was told that it could be more beneficial to have only one letter be from the place I work now (Company A), as having two letters from the same place (but different people) could be seen as redundant. I do have a former employer from "Company B" I could ask (who does have a PhD), and the main work at Company B is tangentially related to what I want to focus on in grad school, but I feel that while the letter will be strong and positive regardless of who it comes from out of these, it could be more beneficial to have a second letter come from Company A. I say this because I have been here longer (15 months vs. 6 months at the previous company) and have therefore taken a larger role, everyone I work with now publishes regularly unlike at Company B where the work was more focused on R&D for product development, and both letter writers at Company A are well-connected in the field and more specifically this particular research topic. Additionally, I feel that the writers at Company A could comment more specifically on my research inclination, while at Company B it would be more focused on technical ability and hard work. Finally, I haven't been in touch with my employer from Company B, and while it would be straightforward to reestablish contact (and I'm sure they would respond positively), this could be considered a disadvantage.
My question is: Despite the fact that a second letter from the company I work for now could be slightly stronger compared to a letter from a previous employer, could having variety in my letters outweigh this?