If it’s of any insight I will give you my experience and perspective on the matter. Do jump to the perspective if you don’t want to hear an epic story.
✯Experience: What happened to me once on Boulder Bay was that there was a 3v3 battle containing team 1 with HRE, Abbasid and Mongol and team 2 with HRE, French and China. One of them in team 2 built a wonder while the Chinese built layers of walls around it and chose a time to attack us together. All of them contributed with stone to those 4 layers of walls fully defended by 1 keep and lots of towers.
Their strategy was to harass so we would build normal counters to what they had, and obviously, we did. But the problem was that they did not have as many units as we assumed due to how they were playing. We were intimidated and got too prepared so they pushed a wave at us and it looked like we won the skirmish but then their China and HRE left the match and their units had to be dealt with one by one as apparently neutral units don’t work to be targeted instantly by ‘‘attack-move’’ command.
That was enough to give us trouble as we lost to a bunch of neutral troops. The trick was that, French was the only one with a full army and no civilians. Which made me suspect that while the skirmish was happening, they gave all resources they could to the french for a last stand.
In the time the wonder was there shaking its timer at our eyes, we had to make a new army and engage the knights and the defenses. And they wouldn’t engage away from their defenses. Seeing that, we didn’t risk an engagement so we put up a plan for the HRE to flank from the sea while we take the enemy attention at the gates.
That’s when we found out the French had an army of 200 knights full. We were overrun at the front gates twice and HRE’s flank got only through the first 3 walls while also being overrun by the french knights. Mind you this was before the latest patch.
So we made an army again and pushed again with mangonels and defeated our side of the knights but we had no siege force, only mangonels. HRE was again flanking but he was overrun yet again, punched through his last wall. Naturally the enemy had around 12 stables ready to make more knights so we had a face-off right at the last wall before reaching the wonder. His knights were reinforced, we ignored most of the towers just to get to the wonder as time was scarce and before you know it…we lost the engagement. 12 mangonels weren’t enough to split between knights and the gate, 2 of them even got stuck in the moshpit. The mongols had more settlers than horses and my HRE was out of boats and gold for another push as he forgot his transports on the shore while we were fighting and got burned. My spearmen were simply not good enough to hold all those knights and protect the mangonels at the same time.
The timer ran out, and defeat was announced. I have a fear of wonders ever since. It was just one wonder, and it was enough to win the game. We had the middle protected by our walls, I made sure we use the market from the beginning and not the enemy. But it was not enough.
► My perspective: Even a wonder per team is easy to defend because one of the players can simply just go turtle. The only counter to a wonder victory is early aggression, especially picking on the weakest enemy as they are usually the turtle who’ll build the wonder. Minutes allocated are also a problem because 15 is not enough for the attacker and more than 15 is too much for the defender. I’ve been on both sides of the barricade where either I or a friend went turtle and we played 3 people pre-made, or we had to face a pre-made team yet again. At the same time, only trebuchets can shoot a wonder down as it’s the only long range siege unit that can throw above walls, otherwise cannon balls go right in the first wall they touch so you can give a wonder 10x the amount of HP it has technically. When going through the enemy base, you have to deal with units otherwise there’s usually x10 barracks that spam units that mass up and will hop on your siege.
So technically, destroying the wonder means winning the game the standard way while also having an extra landmark that forces you to do that.