It's totally possible to have a strong human dps cleric. The -dmg received is actually rather nice for surivability, since the notable dps clerics tend to be targetted first by other magic users. Halfkin does make it easier to cap mcrit rate, but it's possible to cap mcrit rate anyway with the right gears even if you don't have that passive.
That brings racial skills into the picture. For dps clerics, halfkins would have the better racial skills, but you'll find that the halfkin skills are more used in places like arena, or possibly with capping crystals. The reset cd skills does give a nice matk bonus, but Holy Smite (the main skill you'd be spamming) has no cd anyway. Whereas, the cd reset skill itself has a cd of 2 minutes.
The human racial skills won't help you much as a dps cleric either, unless you decided to step out of combat to revive someone (which is really the job of the healing clerics anyway). The skill does give an instant hot but I wouldn't really on that to stay alive.
Long story short: either race can make a good dps cleric in TW. Choose your race based on ALL of your classes, as well as racial crafting. If you are still on the fence about rerolling, look at all of the fame and achievements your human has. Keep in mind that you'd have to earn all of that back again on a new character. If you do make a halfkin, remember that you can archive any orange gear and costumes you have on your human to transfer over.