In fact, any score turned the return game into a nightmare. You have already described 1-0. Now let's say the visitors won 2-1, in which case all they could do was play the bus in the return leg and hope they didn't lose by 2 goals, a 1-0 defeat was completely acceptable. It was a real mockery of football and fans.
And yes, it’s completely absurd when the overall score is, for example, 3-3, but one of the teams goes further “just because.” It's hard for me to praise UEFA here since they just corrected their own mistake, but it's good that it happened.
I hope the same thing will happen with the Swiss system, in my opinion it looks unviable.
I honestly felt differently about a 1-0 back at the time because most of the teams that played in the Champions League knew that they would probably score one goal in the second leg, at least when we reached the round of 16 most of the teams had the quality to score. It destroyed a lot in my opinion. Or let's say it this way, of course when the home team in the second leg scored first then the game was equalized, but the away team still had the chance for the knockout with just a single goal. What's the excitement if the away team scores the 1-1 in the 84th minute? Everyone knew that it was essentially over. This is fundamentally different today, which is good. Even if a team takes the lead in the second leg by one goal, it doesn't matter what minute of the game it is, there is still a chance to counter that goal for the team that fell behind.
What's the deal with the Swiss system? Lol, I feel like a newbie, should I know that?
The strategies were different, but they were all based on the non-equivalence of goals (absurdity, one goal “has more value” than another) and this was unfair.
The Swiss system is just garbage and chaos (for football, for chess it is ideal for holding tournaments with an infinite number of participants). Until the game is played you don't even know your next opponent. After each round, opponents are assigned based on ranking (derived from the results). There are no double games at home - away. Always a new opponent. This is not a group stage, but a group perversion.