Galan007
|Quantum Observer|
It may have seemed to Goku that Beerus was going all-out during the Exhibition Match(because Goku had never seen him fight like that before), but with all the lowkey 'upgrades' Beerus has gotten since then, he probably wasn't.
And aside from the fact that killing was forbidden per the Tournament rules, it's also unlikely that the Destroyers would have actually been trying to kill one another in general, due to the repercussions that would've had to their universes. Incapacitate, yes... But kill? Very doubtful.
So yeah, with all of that considered, it's very likely that Beerus(who was clearly the most powerful Destroyer on the field) was still holding back to some extent... Probably a lot, since many of the other Destroyers almost seemed like fodder in comparison. For example, even when several Destroyers attacked Beerus at the same time, they still couldn't beat him.