There are only 32 direct upgrades in the game.
The Third Degree: With no downsides, the only upside is that this weapon hits enemies that are connected through a Medi-Beam.
The Solem Vow: With no downsides, the only upside is that this weapon shows you the HP of enemies that you are aiming at.
Weapons such as Ali Babas Wee Booties, Targe n' Charge, Kritzkrieg, RazorBack, ect, ect are side grades. Even though they have no downsides (stat wise), they do take up a slot. The Booties take place of your Grenade Launcher, and the shields take up your sticky launcher. Same with the Sniper Backpacks, Soldier Boots, and Heavy Food. The Kritzkrieg (with no down stats) is a side grade as well. It turns your invulnerability into insta crits. The equalizer/escape plan are great melee weapons, but they prevent being healed (and the escape plan makes it so you take Mini-Crits while out), so they are not upgrades.
I hope this cleared up the above answers.