I love the shot gun.  I use shotgun 8 and replaced me plasma with that...  plasma kind of falls off towards the end game.  They are good against shielded things, but there's better weapons.  I would get the missle rack 6 in my opinion.

IMHO, energy 6 weapons are not very useful.  

Anyway,

AT 6 > if one has the +range implant (rare or legendary certainly).  It is too easy to be killed by others and I do not recommend to upgrade energy 6 weapons to higher rank.

MR 6 > I won't recommend.  (But it is still useful in early game.)

In early game, as the bots and humans are still weak.  I used mixed weapons to save resources and I never upgrade energy 6 weapons > 3 stars. 

I personally recommend KS to use Shot gun.  I usually rush and then fire.  Done.  Very effective.  But now the Shotgun has bug.  Better wait till P fixes it.  But I will say, do not let your KS to rush Zep.  The AI Zep is too clever and always stuns you.  

I will consider to use RM in Guardin, Panther or Archanos. RM, now, is a game changer.  But one has to get the + radius (rare or above) implant.  It needs extra a coins.

Save some A coins and get the DL8/RM8.  DL8 is very useful and can be used for a long time.  I put it on my Ares.  RM8 is also good till mid game. A rare or legendary implent is not a must.

One suggestion > while I purchase a weapon, I always check the achivement.  It really helps to get extra rewards.  

I agree.

I like to use Shotgun 8 but is Shotgun 8 in progress path?  I recall (?) it is an event reward (?).  I believe I received it as an event reward some months ago.

I unlocked the SG8 for $3.  Lol  😈