Whether I do it successfully is always an open question--see what you think of your results and let me know if it was successful for you.
I've cooked for a long time. If I am not in a kitchen cooking I create recipes in my head (though I do this even while I'm cooking) and as I put things together in my head I taste them in my head.
For your request that is what I did. I cut the garlic back because I knew I'd be using oil. Some of garlic's flavors are fat soluble and the oil carries them well. The 5 cloves called for in the recipe get minced and worked into 3 lbs of meat; I felt 2-3 cloves in approximately a 1 cup marinade would be garlicky enough. As for the herbs and other seasonings, those amounts work for me as I 'taste' them. I added the granulated onion because its subtle sweetness balances the fresh garlic and the lemon. Thyme works so well with onion and garlic and it and the marjoram balance the oregano which, to me, can take on almost an astrigency, especially when mixed with lemon juice and especially when cooked a long time (you won't be doing that here but still, imo, the marjoram is good for balance as it is a 'sweet' herb).
Marjoram and thyme are very Mediterranean in terms of flavor and use--they are both quite Mexican as well. One sees them in the cuisines of both Greece and Mexico though they are not often identified with either. Though it is quite true that one often sees a mix of olive oil, lemon, oregano, salt and pepper as a marinade for Greek-style lamb (my Greek friends in San Diego use this blend), I find it lacking; I add the other flavors of onion, thyme and marjoram and white pepper because I feel that they fill out the flavor profile nicely. See what you think.
For a rosemary-biased marinade I would do something similar to the one you just did except that I would cut the thyme to 1 t, replace the oregano with an equal amount of minced fresh rosemary, and cut the marjoram to 1 t. I think that this would work well.
See
here for a little more info on how I come up with things and a method you can use to increase your recipe development skills on your own.