You can have both. I have multiple people over? 6 person FFA with the works. Just me and my bro? 1v1 tournament rules lets get sweaty. The diversity of options is what makes Smash such a great game.
Yes time limit, every competitive ruleset has a timer. You need it to prevent stalling and other such poor behavior.
Also, restricting to only battlefield would massively advantage any chars who KO off the top. There’s a list of legal stages for each game to keep things balanced when competing in best of 3+
This is just my preferred rule set for “competitive play” with my friends.
I prefer no time since we won’t really cheese each other and some of the battles end up being fierce.
Battlefield only just saves time from actually picking stages but you’re right about advantages. This really just carried over from our melee days where we always played battlefield.