The ideal offspin action is fidgety. High arm, land on front foot, pivot.
It's because a rubbish offspin action is equivalent to bowling slow cutters, if you want to get a lot of energy and revolutions behind the ball using just your fingers you need to get the whole action right. Look at guys like Swann, Ashwin, Randiv, Ajmal and Harbhajan when they bowl. They all have high arms when they release the ball (Ajmal's is bent, but yea), they pivot off their front foot and drive forward with their legs and hips when releasing the ball, trying to get all that energy into spinning the ball and firing it in.
For legspin, you can lazily amble up to the stumps and let it go, and get a decent about of turn and bounce. You don't need a very powerful action. You try that with offies and you get nothing. Viru ambles in, but he pivots off the front foot too and bowls it quite slow to rip it. The other names mentioned have very energetic actions. Gayle and Pathan amble in and let it go, and they don't get much turn, and fire the ball in using the amazing strength they have in their shoulders, chest and back. Raina has a tidy action too, not too energetic but not too lazy either.
Similarly, look at Vettori, and then contrast that energetic action to slow-pie chuckers like Yuvi and KP. KP is similar to Viru, and Yuvi if he wants to fire it in tends to sling it in and, again, uses his back and shoulders.
So in that sense, yea, Offspin requires more energy to bowl. You can be lazy and get away with accurate, non-threatening offspin at club level. Anyone can roll up and bowl a few overs off offies without wides/fulltosses. But try that at a higher level and you will get spanked, you need a lot of revolutions and energy behind the ball, to get bounce and drift and turn.
But for leggies, the problem is opposite. You'll get all that with a lazy action, you just need to work on landing it right.
So depends what level you're playing at. At club cricket, it's easier to say bowling offies are easier. But at international/domestic level, you could argue it's harder being an offie than a leggie (because by then you're likely to have reasonable control on where the ball lands either way, and thus it's about being able to bowl effectively for long).
Sadly, none of my mates has a garden no where near big enough. Whoa, that's commitment if your actually going to travel all the way just for a few hints. We've got 2, I think, in Warsaw, but it's like a 5-6 hour drive.
, and since leg spin requires patience and hard practice to get it right most of them either concentrate on their batting or start bowling offspin from when they learn to play cricket. So you're pretty much right!
