There's not only the US and the EU system.
I like as well the YeOldeInn Monster Scale someone was bringing up.

1BP

2BP

3BP

1BP

2BP

3BP

4BP

5BP
I was running tests with it and it fits much more the picture i have in my mind for these types of Monsters. Plus it sperates Mummys and Chaos Warriors a little bit. I am really a fan of it.
Back to topic.
Orcs are not built like men. Men are not built like Men. I mean, is the Barbarian 8 times bigger than a Goblin? Is he bigger than the Wizard? No.
Feel free to give an Orc some extra BP or extra defense dices if he is the Boss or even the Warboss.
The Fimirs are interesting because a lot of them have access to a Spells. They might even lead some normal Orc Boyz.
But apart from the normal Boyz, I wouldn't want to bet on the outcome of an Orc Boss fighting a Fimir. I guess they should be in the same strength range, sometimes the Orc Boss is stronger sometimes they are equal.
If you put a Fimir and an Orc Warboss (the really big one) in the ring, fighting each other, I'd bet the Orc Warboss wins 95% of the fights and loses the other 5% only because the Fimir uses dirty magic tricks.
Just think about one thing: Defense dice feel big if you have a lot of them. They also make a big impression on players. But they don't do much harm - you need three of them to equalize a BP - and they are unreliable. Imagine the YeOldeInn Gargoyle with his 5 BP is replacing all BP with Defence Dice - that makes 15 of them.
The YeOldeInn Gargoyle would lose his BP slowly, until finally there is none left; so he is strong, but you can reliably see and end coming sooner or later. If you give him 15 additional Defense dice instead, and 1 BP, it could be that he dies immediately - or in worst case, he could survive eternally, killing the entire group, depending on the luck of the day.
So here's your use - give him Defense Dice to make impression on the players and to give luck a role on the table. Give him Body Points to make him harder and if you want to spare your group unpleasent experiences like in my example.
Last but not least - If the Heroes have some equipment and their stats are, let's say 3/3 or 4/4, the basic Goblin, Orc, Skeleton or Zombie are just useless; worse, it can happen that it is no fun for Morcar anymore to put them on the table. If you want to keep using them, they really should have a little bit of equipment, leveling the Heroe's strong stats a little bit.