I'm happy to give some input.
The tournament's trying to balance community inclusivity and also giving smaller nations a decent chance against the stronger ones. If the team sizes were too small there would be no point in advertising all over the forums and hyping it up, because only a few chosen people would be able to play in it. It's not like Groupfighting tournaments where we can have an unlimited amount of teams, in a nations tournament you can have only 1 team from each nation so to truly involve the community those teams need to be relatively big. It makes it easier for Team Captains to pick their teams too, they have enough spaces to consider different parts of the community without looking too biased. Imagine a UK team of 6 players, we may have 2 17es, 2 Nr24s and 2 92nds, that could be considered biased, but with 16 slots, we have players from 17e, Nr24, 92nd, 22nd, 78th, 77y all included. To truly get the national community involved it has to be a somewhat big event.
We reckon 16 players is enough to give a lot of community members involvement in the tournament whilst also allowing smaller nations to compete. The minimum possible match size is actually 8 vs 8, this is not far off from 6 vs 6, it was decided with smaller nations in mind. So we have actually compromised as much as we can to make the matches smaller for small nations. The maximum match size is 10 vs 10, which allows larger nations to play more of their players when fighting eachother. But I don't want to take away from some of the 'smaller nations', people should keep their eyes on a couple of these 'smaller nations', they could go far in this tournament; Belgium & Russia are doing particularly well at the moment. In the past other 'small nations' have done well, Denmark for example got to the semi-finals of the first NWEC, Finland almost knocked UK out in the 2nd NWEC (it was 11-10) and in McPero's nations tournament Turkey almost knocked out Netherlands (they lost by 1 round I believe). So there is plenty of evidence of 'smaller nations' having a chance at getting far with these sizes.