Actually, people later in the turn order do have an advantage. Let's say someone leaves their border, maybe due to a peace deal, and you attack them in fall. You then gain supply centers and they lose supply centers and armies because they can't react. Basically, they can react better. Of course, people earlier in the turn order do have the advantage you mentioned. And yes, I won because I was able to attack with two armies. Because I was prepared to attack you with those two armies. Your armies were all elsewhere at the start. Yes, the attacker has the advantage, they strike first and likely prepared by moving their armies into position beforehand. Yes, being forced on the defense is a disadvantage. I don't see where you thought I disagreed with you on most of that. You could be ready for war by attacking, which you weren't ready to do because you are actually in a shit position, squashed between me and Luathbas. Lamentia is squashed into a corner by two lords and has no real chance to exploit their advantage of being last in the turn order because of it. On top of that, it's next to a lord that goes at the start of the turn order. Basically, it's in a shitty position next to a lord with a good position and it's difficult for it to prepare properly against it's neighbours. They also have far less freedom because they're squashed. It would likely do better with a bump up in the turn order to make up for that.
Either way, let's see the whole game first before we start thinking about changes. I can imagine things changing when there are fewer players with more armies, and changed mid game will simply mess things up.