<<A ten percent annual yield on investment is a HUGE return, especially in medieval terms. Remember that the idea that the landlord is responsible for maintaining the property is a modern idea.
I'd say that the annual return would be more like 1-2%.>>
If you want to break things down further you can, but I'll start by pointing out that the 10 percent paid in rent is not a 10% return to the owner. If you want to take out repairs/maint. (which you'll have to do anyway, I suggest you leave it in the rent and let the landlord take care of normal wear & tear - otherwise, you'll either hire someone else or do it yourself for similar expense). For the example of a 5000 gp manor house with an annual rent of 500 gp, consider 20% of that repairs & maint., or 100 gp.
Other factors that an owner (not a renter) will have to pay is taxes (another 20% or more depending on the tax), vacancy (the house was probably not occupied all year every year so the income was down, but the repairs maintenance and taxes remained the same.
Final return to the owner is probably closer to 5%. In high demand areas he could do better and vice versa.
I note that this assumes the value of the house remains constant, which will probably be true in most campaigns, but not true in real life.
To me the return sounds really small, but the trick is that there probably aren't a lot of safe alternative investments in your campaign. Do you have banks that offer interest, CDs, etc.? Trading ventures are rife with risk. Businesses could be invested in but probably with similar returns (unless you are into usuary and don't mind destroying the business for short term profit).
Anyway, probably more than most need for their campaigns.