To do both, develop your stroke and use it. If you've never seen it analysed, it's here:get good at 2Ks; lower my SS split for the same times listed above, 60-75 minutes.
https://www.concept2.com/indoor-rowers/ ... que-videos
2k is usually attacked from both ends: a week would include 3, 4 sets of intervals, all done using our best stroke, plus one or two long pieces using the same stroke but at lower rate. If then you can pull an 8W' stroke at 32 in a 2k, that's 250+W and about 7:20.
I'd separate training for ½Ms and the like. I've done that a couple of times, with a few 10ks, then two 1h pieces, then the ½M. This can get you under 90 minutes without too much trouble.