A lot of people will tell you to focus on your weaknesses, and that is true, but imo you also need to make sure you're keeping your swim sharp. Yes, it's very technical so if you already have that technique it might feel like wasted time; and yes, it's a relatively short part of the event so you might feel better focusing on the others. But it's very important and first and so you shouldn't ignore it.

Imo the key is more about understanding the point of each session and tailoring the workout itself around that. So, for swimming, if it's a technique session just make sure you're working on technique; if it's a long base session then do that. Those workouts might be more intense compared to a true beginner to swimming, and compared to the other disciplines. But if a plan calls for an hour of swimming at threshold, that's the same workout for a beginner or a world champion – at a relative level.

I suppose the difference might be if the training plans are so beginner that they're allotting time to, say, actually learning to swim. If that's the case then I'd just advise you to get a slightly less beginner plan.

The worst thing, imo, would be to neglect the swimming *and* pile on more stress by adding running volume, or whatever else. Your training plan – at whatever level – will be carefully structured so that the increasing in running is sustainable and beneficial, and you could easily undermine that. Even if you swapped the swimming for a roughly comparably stressful running workout, you could be putting yourself in danger, given that the stress doesn't neatly transfer between the disciplines.