A max HP-boosted Chomper, such as Mortem or Thor, (8200 HP) with 10 boosts in Attack (~3000 Attack), would only be able to deal ~2250 damage on turn 1 with distraction alone (Ignoring Cleansing Impact, which needs to be removed and replaced with something more fitting of such a High Damage Fierce), 1485 damage with Dodge, and 742 damage with both.
An Erlikospyx with 12 attack boosts (2370 Attack) deals 8295 damage across 2 turns without Revenge, while still having enough HP without any health boosts. The same is true of other Cunnings,
Magnapyritor can kill this same hypothetical Chomper in 2 turns with 14 Attack boosts (2379), but can also reliably kill it in 3 turns with any number of attack boosts greater than 2 (1806 Attack).
Poukandactylus can kill this Hypothetical Chomper in 2 turns with 10 attack boosts (1823 Attack).
This is just a small list. The point being made is that these Cunnings, while investing 10 boosts minimum into speed to counter a potential Nitro Chomper, can still achieve enough damage to kill the highest possible HP your average Chomper can have (Often with boosts to spare). If I were to switch the stats around and pump up attack to maximum levels, then all that would be required would be less Attack investment and more HP investment to achieve the same results. Cunnings are more than strong enough as they are to handle any Fierce without Cleansing access to high damage cleansing moves.
Now imagine the damage or durability that these same Cunnings could have if they didn’t have to allocate 10 boosts into speed, considering they’re strong enough to deal this much damage in 2 turns. That’s why I’m fearful of buffing the speed of the class that focuses on dealing High Damage before their opponent gets a turn.