Nobody in FS ever says something like "I feel like Blaze could win the war by himself, it's scary".
In Ace Combat, your action is the most important, you can and most of the time need to blow up every fighter, tank, guard tower, and battleship yourself. You can essentially ignore any allies as they're either invulnerable as story characters or not important, you can do absolutely everything yourself if you pick a jet with enough missiles. You encounter massive battleship or flying fortresses and proceed to take them down yourself or with a few wingmen. AC is at its core a power fantasy.
Maybe nostalgia goggles are clouding your vision here a bit, because allies at no point matter in any AC game I've played. Maybe some of handheld spinoffs have allies that do something, but I doubt it.
In Freespace you shoot some fighters and some bombers. Sometimes you do a bombing mission where your bombs contribute like 20% of the total damage to a capship. Most of the time you won't have the majority of the kills in a mission. You're not going to take on massive capitalships yourself or with only 1 wing and come out ahead. That's the big difference. You even fail quite a few missions and are completely helpless to do anything. Despite JAD's memery, Alpha 1 is definitely not the crux of the GTVA. The most you do in the retail campaigns is not die while shooting down lots of strikecraft, but you almost always have support from friendly capitalships whose beams will do most of the work against hard targets. Yes, you can get the SJ Sathanas on your fraglist but that's only because beam damage doesn't count for kill awards in retail. You're not really the one who killed it.
Nobody marvels at your skills. Nobody says you can win the war by yourself. Nobody talks about you like they're talking about a superhuman. Nobody is going to call you a demon or feel fear for the first time only in your presence. Enemies aren't going to panic just because you appeared. Freespace presents you with the limits of what a single pilot can do, in both narrative and gameplay.