Sorry looks like I didn't quite make my intention clear. I meant that if you're trying to use it as a battlemagic spell to attack then it requires being in the front-lines.No it doesn't? It kicks in whenever you're attacked. That includes at range, at which point it would charge whoever attacked you and try and murder them. And if you think nobody is taking pot-shots at the enemy Wizards, I think you may be engaging in a bit too much optimism.
However, if you use it defensively then you have to compare it to existing options that can be utilized. In this case that's the just have normal soldiers (or better yet soldiers specifically trained to the purpose). You can mix them up and use both but that adds an element of risk.
In a major battle a wizard is probably gonna have some troops with them and/or between them and the enemy, but that's a bit different than dedicated bodyguards. And as noted, a Red Rider is a lot more hardcore than most bodyguards so this is kind of like saying 'Well, you have light armor, why would you bother getting heavy armor and a shield?' or 'You have a knife, why bother getting a sword?'...sure, you already have something that does something in that area, but this version is a lot more potent.
Rather I'm comparing the potential danger the Rider can cause to your own forces and if it's worth the risk of using when instead you could be using a complement of normal soldiers who have human intelligence and initiative.I think you're vastly overestimating the degree to which wizards are safe from enemy action in a normal battle.
While having the option of the Rider is nice it just seems to me that in a major battle the preference for the average wizard would be to have soldiers working to guard. Mixing in the Rider seems like it would be quite potentially dangerous for reasons like I've previously mentioned (pushing the wizard our of the way, drawing weapons, acting in anyway that might provoke the apparition). Also the Rider doesn't seem like it's great in teamwork and may overrun or get in the way if you tried to mix it with soldiers.
Basically I compare the Rider to having soldiers for protection and judge it as the lesser option. If you lack soldiers for protection or are jumping into the front-lines then that evaluation changes.