A lot of it might be your own connection or interfering signals. If you live in apartments or in heavily populated area and everyone else has wifi and your wii is using your wifi, even if you aren't sharing your connection your wii is getting interference. The only way I was able to get around that is to buy a usb Ethernet adapter and directly hook up my wii u and delete the wireless connection setting. I rarely ever get any errors and only the occasional lagging. I have even had times where everyone else on my team got an error but since my signal was so strong I was the only one left (ended up being 1 v 1 ranked... intense to say the least).
As far as loosing steam, with someone people probably. I imagine more and more people are playing story mode and amiibo challenges. I don't mind only 2 maps per 4 hours though. I do think they should increase levels. No point in playing turf war after level 10, especially of you are skilled and can easily hold your own/pull your weight against level 20s, which I have seen plenty of.
At first I didnt like the fact you couldnt fight with clans in ranked. But the more I play, the more fun it is that way. It could get way too serious otherwise and nintendo seems to want to keep this game as light as possible. Sure its frustrating but you also never know what you are going to get or who on your team.