Let us see…
 
SNIPER:  
Thing about the Sniper. He’s a loner. He stays away from conflict. His job is to keep out of the enemy sights, while only letting them out of his sight to do that. He stays behind the conflict, if just enough to line a good shot. Direct conflict is his enemy - he is literally one of the two weakest classes in the game (tied with the spy) in direct confrontation. His only saving grace is that he can use back-items to boost defense, slowly regenerate HP, or wield a jar of urine to put out fires or mini-crit enemies.
 
Twilight is a leader. She’s scientifically inclined, knows magic, and is a scholar by-and-by. While she is by no means a physical pony, she is not afraid to take charge and rush into danger. She is the pony everypony goes to when there’s a problem; friendship, magic, or eldritch horror related.
 
The Sniper immediately takes away any form of leadership role Twilight could potentially possess. The other classes do not rely on Sniper; he’s useful, but not really necessary. Sure, a wall of Snipers is a deadly thing, but we’re considering a solo concept - one character. Additionally, on a more flavor-based level, the Sniper is perhaps the most mundane class of them all, so Twilight’s status as a magician/scientist is entirely ignored.
 
That’s my opinion though.