I haven't said they weren't. All I am going off is what I've encountered so far. But cheers for the comment.
All I said was that 160 HP might be better. I could be wrong.
This just allows faster percentage recovery, since Bronzong already has high defenses which are getting to +6, I'm not sure how important the HP value will be, unless the opponent scores a critical, in which the sub breaks and Bronzong is healed by leftovers.
I also believe that the extra EVs would be well placed on Defense, this is because Shuckle's team consists of
Shuckle,
Power Split - Lowers Offensive stats
Struggle Bug - Lowers SpA
Rest - Reset Sturdy/recovery
Gastro Acid - Ability removal for things like Clear Body
Gastrodon
Flash - Lowers accuracy
Recover - Helps gets off multiple Flashes/Rock Tombs
Memento - -2 Att/SpA
Rock Tomb - Lowers Speed
Now what is missing here? A pure Attack lowering stat that isn't a one off move, such as Charm.
The enemy pokemon would already have about 1/4 of their original Att/SpA from 2 Power Splits.
-2 Att from Memento
-6 SpA from Stuggle Bug
Since the stat lowers was quite uneven, I would place the extra EVs on Defense. Making it 134 SpD and 151 Defense
Now, this is honestly doesn't matter that much. All my EV set offered is getting fully recovered from Substitute 1 turn earlier. The only real way that the first enemy pokemon is breaking through Bronzong's sub is by getting a crit or being a crazily powerful physical Fire type. And even then, Bronzong can just use a few Iron Defenses and be fine.
I understand your's (well, Shuckle's) EV setup too, more HP means more to chew through before the sub breaks, but I don't really see much breaking that sub in 1, or even 2 turns once the boosts get going. Also -
252 HP EVs gives a sub 43 HP
140 HP EVs gives a sub 40 HP
This tiny difference is why you made me lol
-edit-
Shuckle should at least consider reducing the HP EVs to the bare minimum for a 43 HP Substitute.