Honestly, i think most people don't use assault weapons correctly. it tends to be best used when you've got other mech supporting you or a good position.
Example; weapons like plasma and fusion cannon are best used in close to mid rang together with a mech that can give a boost to their abilities, usually being used in my closed off places or while protected by a pleayer.
Example 2: weapons lile auto cannon and pulse cannon tend to be best used either together with another weapon or as a supportive weapon from almost long-ish rang and medium rang using more tanky or agile mechs.
However, in each case the problem tends to be that guided weapons destroy users that use them like this or mechs with high hp and/or dash ability get close in with high damage weapons and thus take the players down, which causes the weapons to have a drastic decrease in use.
If there was something to make up for this than i think they'd be far more useful, perhaps neutral mods that include both a possitive and negative effect such as a mod that increases the time needed to lock onto you but if you use guided weapons it will also make it so that you need more time to lock onto mechs with guided weapons