i never played academy... i understand that when a pest creature attacks, it must atttack the guard, but the guard can ignore it: no couterstrike, no guard counter removing.
i agree that it would be simpler if all the functionnalities would be the same (for siituations that occure in both games, of cours).
but why is this pest-guard rule better than the arena one?
in a game point of view, this rule makes the pests weaker. are they too powerfull in arena?
in a background point of view, the guard is occupying the zone, so all cratures must attack it, after an attack the guard had to concentrate on the attack so the zone is free for other creatures. why would the guard be able to ignore a little creature more than a big one?
For exactly the reason you describe. If I'm guarding a zone and there's a giant ogre with a club ready to strike me, and there's a ferret with 2 teeth, and the ferret bites me in the ankle, do you really expect me to turn my back on the ogre to swing at the ferret and exhaust myself on the process? Personally I'd hope I have the fortitude to ignore the ferret bite and keep my attention on the ogre.
So... perhaps it isn't a "better" rule (as you mention, I don't think anybody thought pests were overpowered in Arena), but it makes a lot of sense thematically.
As for rules differences, there are several, most notably (1) No planning phase (you fetch a spell immediately before playing it), and (2) no quickcast phases (so you can play a full action + quickcast to end a round, then have initiative and take a full action + another quickcast, all before your opponent has an opportunity to take even a quickcast let alone a full action).
Oh, and everything happens in the same zone, so guarding and eliminating guards (by hitting them or by Staggering them or by making them Pests via Shrink, etc) is really important.