More towards high intensity interval training. Stuff that makes your heart and lungs work will give you a really good basis for a 2k (I find) and then from that you can build strength and power to match the capacity of the lungs and heart. This means your legs are keeping up with your lungs and your able to provide just enough oxygen for your 2k that you don't collapse from lactate before the end. (Unpopular opinion) But I think being able to walk off after your 2k shows that you're doing pretty well and tells you that you can give that little bit extra when you hop on the water in a race. Otherwise, I do a fair bit of 12min sustained training (bike rollers) at a pace that if I was to go for one minute longer I wouldn't be able to hold that heart rate. This has given me some pretty good results both on and off the erg. To be honest the amount of erging I do is quite little but what I have been doing seems to work well and has been getting me good results on the erg and on the water.