Take a not very useful MLRS, nearly double it's price, and give it no major advantage.
I agree with you that the B-21 and the RM-70 aren't very useful. They are so unaccurate and weak that making them firing is just a waste of supplies. It bothers me because I think it was much more useful in real life and because, on a emotional ground, I like the RM-70. It looks like a MLRS should look and it seems powerful when you look at it. But, when you see the price and the actual firepower, you never use it again except for flavor in single player.
About the Strela 10, I don't understand why it's so inaccurate. It's even more unaccurate that the MANPAD Strela 3. It's a waste of deployment points. The OSA AKM is much better.