There should have been main characters there so that people care about the battle. The way it's set up now, it's just empty spectacle lacking almost any emotional engagement.
In short, who are these people, and why should I care?
Heck you can say that about the protagonists. They had a pathetic amount of backstory, and yet you cared about them? I mean that heavy weapons guy, I still don't know his name, his backstory was basically "I'm with him." and he tilts his head at Chirrut. We learn nothing of him, AT ALL, and yet you, I assume, cared when he died? Why? He was just as developed as the people on those ships, by that I mean, not at all.
Heck the only person in that movie I DID care about, was that nameless Rebel mook who stuck the data through the door, screaming for help while Vader approaches him from...behind!
While I found the entire movie uninteresting, I challenge the idea that the only time you can care about a conflict in a story, is if there is a main character in the mix. Rogue 1 was finally able to invest me emotionally in their conflict, with an extra, who had 2 minutes of screen time, and likely didn't have a name other than "Dude who died from vader" or "got pwned from behind through the door" or "Guy who handed off plans". THAT guy, I actually cared about, don't ask me why, I couldn't really explain it, but he was the only time in that whole movie that I actually cared what was happening.
So yeah, you don't have to have a main character for it to be important, or investing, it just has to be done well.