Saeviomagy:
In this case, I share your concern. After thinking about it, I came up with a few mitigating factors, however. I do think that Sunder was made a bunch more powerful (likely since no PC in their right mind ever took it in D&D), but I think that there are still some factors that make it less powerful than one might worry.
1) Sunder is less available than it looks. No class in the book gets Sunder as a bonus feat. As someone who's currently building 6 PCs while getting ready to DM a one-shot, I can tell you that those "pick anything" feat slots get filled up quick with goodies. Only someone who's really into the Sundering concept is gonna bother getting this feat instead of, say, Heroic Surge. Or adding in another gun feat. Or taking Elusive Target or Unbalance Opponent as early as possible.
2) Sunder is necessary for most melee weapons to damage equipment. A baseball bat wielded by a person with average strength has only a 1 in 6 chance of doing any damage to a gun. (Bat, as a club, does 1d6 -- gun has hardness 5).
3) For the high-damage melee folks, like the high-level martial artist or the Strong Hero/Soldier who takes the Chainsaw as his specialty weapon, bear in mind that they get VERY LITTLE ELSE.
3a) This speaks to a difference between D&D and d20 for me. In D&D, I always thought that the assumption was that multiclassing was good for flavor purposes, but if you really wanted to be powerful, you went straight up in something. With d20, I think that the designers intended for folks to have at LEAST three classes. A tenth-level Strong Hero with no other classes is a physical powerhouse who can do almost nothing except hit things real well. In a balanced campaign, he's got one or two shining moments a session, when the party gets into a fight and the bad guys are in a melee-able location. With guns as the weapons of choice in a d20 Modern campaign, that's by no means a certainty.
3b) This, I think, is the answer to the dual complaints of "My Fast/Tough/Infiltrator is nowhere near as good at combat as my Rogue was!" and "My Strong/Martial Artist isn't good at anything but combat!" The first complaint overlooks the fact that d20 makes heroes a lot more vulnerable, and consequently makes combat characters a lot tougher to create. The second complaint overlooks the fact that the player building that Strong/MA character obviously did it on purpose, and they should be satisfied with what they created: A narrow-purpose, extremely focused character.
Anyway, that's how I feel after thinking about it a bit, but I'll see how it goes after a few sessions with Tank McGinty, Sundering Guy.
-Tacky