I'm still flying the Cas because I started a new character and have progressed slowly. I'm level 8 but not a multimillionaire yet because i haven't spammed Rhan babies at Breedwell. Thus, I've not afforded the a MS-XI (which is my fav ship). I've not progressed beyond Myrillion yet so I've not gotten the Blade or Sidewinder, which while technically better than the MS-XI, I don't find them as 'fun'/ 'unique' as the other ships. The Blade, because I can't rename it something super cheesy (like the Silverbullet or the Cherrypicker) and the Sidewinder...I'm not sure why I don't like it as well, but I don't-maybe because the interior descriptions aren't done.
Honestly, until now, I've not found a ship I couldn't beat with the Cas...although, in the early days of playing there was a pirate that'd sometimes pop up that I couldn't defeat. I've not seen that ship in a long time, and many characters, tho. I can take out the corvette over the last planet with two machineguns, improved evasion and power core tuners, although, I usually use the MS-XI for that battle. The battle over Zeng Shi can be hard in the Cas (if you don't give the passcode) but not undoable.
Anyhow, thanks for the hint. I have, on more than one occasion, however, depleted all of K7 shields and roughly half her armor without her surrendering. Still, your method sounds FAR superior to what I've been trying to do.