Clearly I am in the minority, but I loved this mode and will be very sad to see it go. I play maybe 2-3 online tournaments a day, and really enjoy that you are trying to climb a bracket rather than just the fairly stake-less FG 1v1s. It's also nice to be able to play For Fun games which are extremely unlikely to be filled with people who will troll and go 3 vs 1, and to have the tournament conclude with 1v1 with items all stages for a change of pace. I also realize most people don't care about win rate stats in FG but for whatever reason I'm focused on it, and playing tournaments allows me to try new characters without worrying about it effecting win rate. You can also play FG 4 person FFA games without it being time rules. I was winning about 75% of the tournaments I played, which was rewarding and encouraged me to go to real life tournaments (where I haven't done nearly as well, but that's another story).
My point is, this mode had some nice advantages and can help be a bridge for casual players to get more into the competitive scene. In SoCal I was having very few issues with bad lag or not being able to find active tournaments unless it was like 3 in the morning. As someone who works full time and doesn't have a super convenient local tournament to go to, this mode definitely did fill a gap and have value for some people, and I could honestly see myself playing Smash less with this gone. I guess I don't understand the thinking behind removing it from the game- if you hate it, you can just never use it, and if you love it, it's there for you.