A lot of your points are solid but I wouldn't compare it to football players having to play their games on baseball diamonds, I would compare it to baseball players playing their games on baseball diamonds because in baseball, all the parks are different and you don't see baseball players complaining that there needs to be a change to the sport to make all parks the exact same. The players embrace it and they like it because its what makes their sport unique and gives a new dynamic to certain pitchers, fielders, and batters that make some stronger and some weaker and the sport more complex and interesting. Different parks give the players a true home field advantage, and I like to think its the same with stages. Having a counterpick makes it feel like its your home field, you know you're in it and if you can just steal a game at their home field, you can win the world series of smash. The game doesn't change entirely, its still the same game with the same strategies and the same play style, but theres small variations that can make the game more exciting and require better management. The counterpick removes a specific combo or makes a move less useful, it doesn't turn the game upside down. If you have a pitcher that is susceptible to home runs and you're playing in a short park, you don't want him pitching because he can take a beating there, so you manage your pitching rotation to work around it or take the loss and beat him at your home field. If you have a character that is strong on the ground and dies off stage and you're counterpicked to a stage that doesn't allow for a good ground game and its played mostly off stage (peachs) then you have to manage your character selection or take the loss and beat him back at dreamland.
A counterpick doesn't win the set, it just keeps you in the game and gives you a chance to get back in it and figure out your opponent and change momentum. If its DL only, and you lose the first match, for spectators its not as much fun because you can realistically predict the outcome, 2-0. But with a counterpick you say ok, this guys taking game 2, game 3 will be back at DL but game 3 is a coin flip, if he does enough in game 2 he can get in the other guys head and steal 3 to grab the set. It adds composure and an extra element to the mind game. Its like kicking a field goal early in football when you're down on the scoreboard. The field goal isn't going to win the game, theres still more to play, but the field goal gives you momentum, it gets in the opponents head, it keeps the win in sight and it gives you a chance to figure it out and rally for a win. DL only is like touchdown only in football, its great for Madden (friendlies) but in the competitive world (tournaments) it makes it hard to keep the game competitive because it will typically be first score wins.
The way I see all this movement towards communist uniformity is everyone trying to make the game like chess. Every person has the exact same starting position, exact same moveset, exact same board, the only variable is the person himself. If thats how everyone wants it then why don't you all become communists and play chess like Garry Kasparov? Or simply play the game with TAS and each player picks what they will do, advance the game a frame, pick next move, advance the game a frame, so on and so forth until a winner is decided. Smash is LIKE chess, not smash IS chess.