I guess I just liked that rounds did make solo matches feel different from the rest of the game (2 nd 3v3). (...) It was almost like playing two different games
Interesting that you say that. For me it is pretty much the other way around. Previously 1v1 had the the same rules as team vs team, only with a forced ft2. Now 1v1 feels like a whole new mode, characterised by one timer yet two health bars and a "half KO" when the first one runs out.
This is perhaps besides the which-mode-is-better thing for others, but downs introduced a little detail I like. It is similar to a situation that when a worse and better player match up against each other with teams, the worse can still grab the small victory of KOing one char from his opponent's team.
Previously when the first 1v1 round showed one player is visibly better, the second round was likely not very entertaining for any of the sides - both just wanted to get it over with. Now, thanks to downs, when one player is clearly better than the other in 1v1, the worse one can aim for the mini goal of "deplete one of my opponent's health bars", and the better one, if he wishes, can aim for "KO my opponent twice without being KO'd once".
It's like a new unwritten mode of "play with a disadvantage against a less skilled player" for the better player and "defeat a super powered opponent while having double health" for the worse one. And that can very well make playing with friends (a situation where visible skill discrepancy is often a thing) more enjoyable. "I KO'd you once!" just feels more like an achievement than "I brought you down to 50% health". That being said, the change should not only make 1v1 more fair but more fun as well.
Sorry for the long post, but hopefully it will make it possible for you to look at the new mode in a brighter light.