Well, invasions, especially in Dark Souls, are highly biased towards the invader. He will have better gear, and that makes a huge difference. While skill can overcome a handicap of weaker gear, it makes little difference when you die in just one or two hits.
I still say they should get rid of "level" based invasions entirely and make it more about power rating or something. Take the amount of damage you can do and what weapons you invade with, and that determines who you invade. Of course, if you want to invade in early game areas, you can simply choose weaker weapons to take with you. I highly doubt anything like this would happen though.
Or maybe they should just stop putting in anything that doesn't scale with level. Get rid of any elemental weapons, make pyromancy scale with a stat, whatever. That way, everyone has to make a fair build and not just a vitality/end build that uses lightning weapons. At higher levels, things are more even, but anything lower than level 60 or 70 is just too vulnerable to elemental weapons and pyromancy.