I would check with graduated students at the dev program to make sure collaboration is actually happening as well as what the environment of the department is when it’s not interview day. Most programs oversell their benefits and strengths on interview days. Graduated students will have a more honest and clear view of the program as well as what the true strengths and weaknesses are.
You can also ask them about their job prospects and whether the rank/reputation of their program seemed to play a role.