I agree with some of what you said, disagree on a couple points. First, in my opinion the 23E is the pinnacle of HK sear hosts/MGs. I absolutely love mine. Second, 100-200 yards is absolutely fine for 5.56. I’ve shot my 23E out to 500 yards and it’s fun. At 200 yards it’s great fun to drop 2-4 round bursts onto steel. Third, the 21E in 308 is also fantastic, though a bit of a rougher ride. That said I can make 2-3 round bursts hit onto steel at 200 yards off hand and am even better off the tripod. The 21E is absolutely worth owning, though for a little more than the cost of the 21E conversion parts, one can buy a 21 host built using the FMP parts kits that were recently imported.
Mike/MM has a great reputation and has piles of spare parts. He’s also easy to get ahold of and provides outstanding customer service.
@NickFromAK you should pick up an HK sear if you can. The mp5 is hands down my favorite SMG to shoot. And then you can use it in your mm23E.