Absolutely. Honestly, with it fully upgraded if you're trying to play through levels with the best rank possible, without wigs and without the Fox Blade, the Murasama is your safest bet in terms of main weapons in many circumstances. The increased damage, speed and (I believe) range make it a formidable weapon while succumbing to almost none of the others' weaknesses when fully upgraded. The armour breaker is quite strong in certain situations too but overall I'd concur with your statement that the Murasama is the best main weapon. If you have BP to spend on upgrades, I'd upgrade that before anything else.
Also, I'm just wondering, how are you meant to No Damage R-04's lobby without the wigs? I hadn't been using any of the 'cheat' items or weapons (well, the Fox Blade) up to that point in my Revengeance run but I had (and still have) absolutely no idea as to how one can beat the GRAD (by EM grenade-RPG locking it) at the end without it, let alone everything else. Do the weapons on the shelves/racks regenerate when you're empty?
I used the wig for that part but I actually don't think I needed it. For the most part it came down to learning where every enemy spawned and shooting the crap out of them. I actually beat the GRAD with the turrets. It was a huge pain in the ass. I didn't know I could just EMP it and rocket it to death.