Mike's right - SIG's got the best balsa around. That Dubro slot-cutter set's been on my workbench for over 30 years. Wouldn't cut a slot without it. I learned though, that the best way to cut large slots (the largest size in the set) is to just push that big one in to the point of the "V" to mark the location, then use the smallest twice to actually cut the slot. This has worked for me for ages.
One of the reasons that you perceive the bow to be not all that bad (which it wasn't) is because you're taking just a bit of wood from both ends. Doesn't take very much to get rid of that gap on the table.