I have a bit newer C30 but I've looked at quite a few and yes, what you have is probably what the boat came with.
I converted to an adjustable topping lift but soon found adjustment is not needed for it to work as a topping lift.
As others have said, it's purpose is to hold the boom up when the sail is down.
I set mine so the boom has a slightly greater angle than 90 deg to the mast. In other words, the boom angles down slightly but still gives me more than 6' headroom.
When I raise the main sail, the sail pulls the boom up to about 90 deg or slightly less and the topping lift goes slack. I drop the sail and the topping lift keeps it out of the cockpit. That is how it should work.
I strongly disagree with the idea of detaching the topping lift from the boom after you have raised the sail. That works for small boats where no one sits or stands under the boom but not on a larger boat like a C30 where the heavy boom will drop several feet. If you forget to reattach it and let the sail drop, the boom could cause injury to anyone in the cockpit when it comes down. There is no need to take that risk. Leave the topping attached to the boom when the sail it up.
I believe you have a couple of options:
1. Repair or replace the clasp. A carabiner or shackle will work. Since the topping lift is slack when your main sail is raised, it is not too short. If the boom is too low in the cockpit you can try to shorten the connection but do not shorten it enough so it supports the boom when the sail is raised.
2. Do as
@justsomeguy suggested. Arranged some blocks at the bottom of the topping lift so that you can adjust it.
3. If you are going to do anything at the masthead, inspected the mast head to see if it has room for you to add a second sheave (pulley) next to the sheave for main halyard. I know later C30s have 3 masthead sheaves installed, one for the main halyard and two for jib/Genoa halyards. You can easily add a 4th sheave so you have two mainsail halyards. I did this and use one for the adjustable topping lift. No real need to add an external block at the masthead for this unless your masthead will not accommodate a 4th sheave.
Some sailors do adjust the topping lift as a sail trim tool, using it to lift the boom to give the sail some additional belly in light winds. There are a lot of other sail trim controls to learn first.
Rigid Vangs are nice and I agree with
@Stu Jackson that Garhauer Marine is the place to go for that option but I'm sure you have other things to spend your money on so pass on the rigid vang for a while. It is a nicety, not a requirement.
Do consider Garhauer Marine for blocks and such. Quality parts for low cost.
Welcome to the forum and to C30 ownership!!!