Hello My Lord ,

When you upgrade a unit,  the bonus reached  is applied to all your units , so the units which you will receive like rewards from the brawl will have the same power ( the lvl of your upgrade).

Esample : if you upgraded the grifins at lvl 32 and have the power = 2300 , than also the grifins which you will claim from the brawl rewards will have the same power, nothing more nothing less ! I hope i explained well ...

I wish you a good day and good game !

I think you nailed it Mic999 ! 

All units that are attached to your account have the same power. 

But  units other people send to your castle  their strength is based on the Lost arts upgrades they have done. so they maybe weaker or stronger to some degree depending on many factors within their accounts. (Boost, Unit upgrades,  the list goes on.)

Yep this is correct, troops are the same regardless of where you got them from.  

The game shows you the power of your units, when you are in castle, catcombs, garisson and in the middle of sending to anything.

All the troops of the same types whether, trained, bought, provided as gifts or otherwise as shown in one stack all with the same bonuses applied. So you can see that they are all treated the same regardless of orgin.

Only different variants of troops have different powers e.g. dark and eldirtch dragons have different power than normal ones.

Also you can click on the troop and it will take you to a more detailed screen showing their power and if you hover over the power a tooltip will pop up setting out what bonuses are being applied to those troops. Very handy but not something you necessarily will notice when you start the game.

Yeah that's definitely helpful to know where the bonuses to your troops come from, they should add an icon or something to let people know about that feature instead of it being pretty much completely hidden.