They haven't hidden their power, but rather team power doesn't play that large of a role in damage output.  I can see the in the above screenshot that Kael did all of the damage, so I bet the following happened:

• High Khatun went first with an incrediably high amount of speed, and increased turn meter for the rest of the team
• Dazdurk went second, increasing turn meter again and also putting a 50% increased attack to the team
• Warmaiden went third, using her AOE attack to decrease your entire teams defense by 60%
• Kael went last and nuked everyone

Kael would be decked out with 100% crit chance, and as much crit damage as he could get.  He also wouldn't have a lot of speed as his turn meter would be boosted by HK and Dazdurk.  The rest of the team could have little power

This is a pretty standard Areana nuke team, and why the speed wars is so important

I understand that and it did happen like this. But I got wiped out by others half my power who didn't beat me in speed. So I should have nuked them with Ithos and finished with Jintoro. Only, they survived my attacks. Power should count for something also, right? If you're faster AND stronger, you should win.

Power  only  goes  for  the  stats  that  kill  and  keep  alive.  Speed  means  nothing  if  you  can't  kill  the  enemy.  Thats  why  speed  isnt  a  bigger  factor  in  power.

This is just a guess but possibly other enhancements such as masteries and GREAT HALL boosts can contribute huge to perceived power but not actually show up in a champs power numbers.  Right or wrong?

Those  boost  stats  so  it  should  affect  power.

They absolutely show up in champ power. You can see their effect by clicking on the full stat info of your champ.

I see from the "total stats" that GH and Masteries make a contribution. But masteries are tricky cuz there are many that are not stat related, but can effect the game actions significantly.

One common trap at least for beginners is the "early nuke" team of spirithost, diabolist, warmaiden and starter champ.  That combo can be real low power, the first two can get by on L30, but can whack pretty hard when def is down.