This is why you just quit til you get thief.

The most itself doesn't lead to very easy balancing.

if you add even 1 more guardian, the thieves will be at a disadvantage. If you decrease the time, you just made it so it's very likely thief will be at a disadvantage.

You basically flip from Thief dominating to thief losing most games.

There are things they could do to help a bit without completely vaulting the mode and redoing it.

Guardians cannot hit the button anymore, the button can be jumped on still but will not go down.

Ever so slightly increase the cooldown between button hits for thief. Not enough where it's basically a complete screw over but enough where guardians say capture 4, the button is hit, and the guardians recapture 4 again, and the button is back up. It leads to a loop where the guardians have to choose between guarding the button or guarding the candy. Either way it's a lose-lose. But a slight cooldown increase on the button could be just what it needs, like I dunno how long it currently is but let's say it's 20 seconds between button presses, increase that to say 25. It's not a drastic increase but enough where the guardians don't have to constantly baby sit the button.

Make it so candy "respawns" if out too long. A common strat is for the thieves to just throw the candy out and hope a team mate comes and gets it. Well let's say after a certain amount of time, the candy disappears and goes back to its spawn point.