Both Of those mechs excel in 1 on 1 stand up fights.  They want to fight you in open style ares becuase their abilities give them advantages.  However, in prolonged hit and run style fights or in close quarters they suffer greatly.  Their mobility is taken away and they can dash into a corner or their shield is useless if they are being attacked from the side or back.

Just have to know how to fight them and with what mech/weapon

I know how to fight with Killshot. The problem is how most people fight on Killshot. 2 Javlin Racks and a Killshot is all you need to secure an instant kill onto a mech with low hp and armour (which is a lot)