Does it make sense for a fast 25-year old triathlete to lift?

It depends. If your goal is simply to get faster then no. If you want better all around fitness, then yes. It wont neccesarily make you any slower, but can help with recovery and general fitness.

One legged deadlifts are good. You can keep it simple, pushups, pullups, chinups,dips, good mornings. Or just focus on muscles that may not get used much. You use your shoulders a lot during swimming but only in one motion, not to the side. So you can focus like that. I would say do it minimally. At least thats what I do. I am just a bit slower than you, but I like to carry the groceries and plan with my daughter (also just a bit older).

I would never suggest against weight training but with your schedule/ability/goals it might be better for you to focus on your goals and improve your swimming. I do think that you could do work to strengthen your core, shoulders and legs that would benefit your swim. I think adding a couple sessions with kettelbells would help a lot.

Also squat more.

That said you are at a much higher level than I so I think you should trust yourself and how you feel doing that much volume. Lifting could be too much if not done sparingly.