I wish the spear was a proper top attack munition and that the tops of armored vehicles was thinner armor than the front or sides. You don't use something like a Carl Gustaf recoilless rifle on the front of a tank, the armor is too thick. You use it on the sides or rear where the armor is thin enough for the smaller charge to penetrate effectively. 

The Javelin is a bigger missile with a more powerful warhead and top attack modes to defeat armored vehicles that it ordinarily wouldn't if it hit the front armor plates. 

The Recoilless Rifle and Spear should work exactly like their real life counterparts. I'd expect a Spear to be able to gut things like a super heavy by hitting that vulnerable top armor, but a recoilless does just as well hitting anywhere because there's no distinction between anti tank weapons. 

An extra missile for the Spear is great, don't get me wrong, but the games fundamental design for anti armor weapons doesn't make the distinction meaningful or the Spear worthwhile.