Are snipers the most lethal threat on the battlefield?

 No, not even close.

To keep this in the spirit of the question, I’ll restrict it to land warfare in a combat zone.

This is Simo Häyhä, the sniper with the most kills in the world at 500+.

Killing 500 men is no small feat and it’s even more impressive that he accomplished it in less than 4 months. That is well beyond what most other snipers have for kills. For example, Chris Kyle only had 160 kills and that was over a period of years.

But this guy…

he’s a forward observer for the artillery. He can call in rounds and take out a whole company of 100+ men with just one fire mission. He’ll do this again and again, sometimes targeting a company, sometimes just a platoon, but each time he adds another bunch to the tally. I have no idea what his name is, but you can reasonably assume he is responsible for the deaths of more than a thousand men and the maiming and removal from the battlefield of thousands more.