It does not destroy the sniper's advantage. Unless the game adds a huge blinking neon-bright arrow to any player with a sniperrifle it won't matter one iota how bright the trail is since you'd already be fragged.
Besides ... there's nothing stopping you from switching to an 'invisible' weapon using the LtG merely because of its zoom-feature.
Never mind that the long range kills are the least of your worries. At short range the visibility of the trail is of no consequence, which leaves you with an extremely lethal weapon that can't be countered except by artificial rules (like an extra long weaponswitch, low RoF) or scarce resources (ie : very few ammo-pickups).
Besides ... there's nothing stopping you from switching to an 'invisible' weapon using the LtG merely because of its zoom-feature.
Never mind that the long range kills are the least of your worries. At short range the visibility of the trail is of no consequence, which leaves you with an extremely lethal weapon that can't be countered except by artificial rules (like an extra long weaponswitch, low RoF) or scarce resources (ie : very few ammo-pickups).