Look at the state of it
Currently in Strategus battles, an army of 2000 versus an army of 500 will still be presented by 51 players vs 51 players.
This creates a problem, because a smaller army is able to kill much more of a much greater army than they should be able to realistically, because they have the same amount of troops present on the field of battle as the greater army. This causes the greater army to endure losses it simply should not, unless it was really, really bad.
A larger army can afford to be more experimental. It can create groups meant for flanking, stealing the flag, diversion, you name it. Having the superior number of troops allow you to fight in a different way than you would if you had an equal amount, or if you were outnumbered.
A smaller army has to be more tactical, has to bottleneck the enemy, play smart, fight for every inch of ground. They also have the huge disadvantage of being outnumbered, this SHOULD give them a tactical disadvantage.
Currently in the 51 vs. 51 mode, if a smaller army of 250 is against an army of 500, if the smaller army had some extremely skilled duelist, they could win, or make a really big dent in the larger army of 500. While this is not necessarily all that bad, and while skill should of course play a role in CRPG, we have to remember that simply outnumbering an opponent is more importan than skill. If 10 pikemen surround Deserter_Mighty_Shaman, despite his skills, he will be killed relatively easy, probably without any casualties. The game should reflect this. In war tactics are more important than skills.
Give me the numbers
When I first wrote this post I was saying that the army with the higher percentage of troops should have the number of players that their troop superiority reflected e.g. If an army of 1000 was facing an army of 500, the army of thousand would own 75% of the total troops, and as such they should be allowed to recruit 75% of the players, which would amount to 76~ players. If the greater army had 90% of the troops they would be able to recruit 91~ of the 102 players.
At first I thought that was a good idea but I realized that it might not be very fun when you're outnumbered so badly that you are down to 10 players on your team. So being enlightened by the people in this thread, I thought about it and my conclusion was that the optimal number would be that up to 25 players was up for grabs for the army with the superior number of troops. How many of the 25 the bigger army would be able to recruit, would be determined by how much more troops their army has compared to the lesser army.
The closer two armies are in troops, the closer the amount of players they can recruit would be. Two armies of truly equal troop sizes would still be 51 vs. 51.
This would mean that a vastly superior army would have 76~ players while the inferior army would have ~26 players. This would create a battle where the troop size is reflected, and give the realistic and immersive advantages and disadvantages, whilst still allowing the smaller army to have a good base of 26 players, enabling it to still play tactically, and still have a chance to win if they were extremely good tactically and very skilled as well.
Why? Because it's fun
The most imporant point, and why I came to thinking about this in the first place, is that it would quite simply be much more fun this way. The commanders would have to adjust their tactics to how many troops they had, this would result in battles with much more variety than we see today.
The forces would certainly feel the immersive difference; a superior number of troops would make the army feel as if they were swarming over the enemy like locusts, while a smaller army would really feel like they had to play extremely skillfully and tactically, and fight for every inch of ground. It would immerse us much more in the battles, and we would truly feel the difference of facing a greater or lesser army.
It would also lend a whole lot more fun to sieges, who are currently very unfair to the attackers. Sieges are places where having a greater amount of troops present is a necessity, you need to attack several directions at once if you want to get in; tactics are quintessential to victory.
Overall I suggest this change because it would be realistic, it would be heaps of fun, and it would bring much greater variety in the battles we see everyday, and most importantly, it would allow tactics to have a much greater importance and depth, and allow commanders to truly shine like they did on the battlefields of old.
- Rewrote the original post as some people here changed my opinion and to make it easier on the eyes.