False equivalence.
The commoner railgun does not merely 'follow the rules'. The commoner railgun fails because 'following the rules' results in the last commoner in the line receiving the object. Any thoughts on the object's imagined velocity are NOT 'rules', therefore the DM just has to follow the rules and the object ends up in the hands of the last commoner. Even that is ignoring the fact that the DM is already allowed to set a limit on the number of Free Actions allowed in the round, and that is built into the Free Action rule itself, no 'rule zero' needed. This was 3e, remember?
Pun-Pun is the same. Sure, plenty of rules ARE being followed, but the whole thing relies on Divine Ranks stacking to make Pun-Pun so powerful. But Divine Ranks don't stack. The DM doesn't need to rule inconsistently in order to show that Pun-Pun doesn't happen.
Those exploits rely on more than just following rules, they rely on assumptions beyond the rules.
But there is no such thing going on here. Chickens really are 'creatures'. They really ARE a valid target for hex. There are no assumptions beyond this; no real-life velocity calculations, no invalid stacking, no assumptions outside the strict parameters of the spell.
It's not an 'exploit', it's just that some people don't like it! That's not a rules problem, that's a 'you' problem.