Moving plants around is the name of the game! I am always rearranging plants! That is what happens when you plant things you don't know. Anyway, half the time the tag and catalog sizes don't work out.
Magnolia Macrophyllia is not a tree I am familiar with but it is suppose to get to 40-60'. So you decide if you want that 10' from the house or pool! I don't know how many years that would take. Your best bet is on the tree forum. Michael Dirr writes that it is a difficult plant to mix in with the home landscape because of the large leaf texture but I would take that with a grain of salt. He mentions its best on a campus or some lawn type setting. Maybe this could be your curb-side tree? Do you like raking 3' leaves in the fall? Lol! My husband would bring it up any chance he got. Is it a hazard for bike riders? Could make an interesting garland maybe but who has time for that.
Here is what Fair Weather Gardens puts in their catalog. Note they also have a supposedly dwarf form - Magnolia ashei:

Magnolia macrophylla - Magnolia
With immense leaves up to 3 feet long and fragrant flowers a foot or more across, Magnolia macrophylla challenges the vocabulary of the catalogue writer! Suffice it to say, this is the largest-leaved hardy tree that we know of! In keeping with its elephantine parts, it reaches 40-50 feet and is suitable for larger properties. In spite of its exotic appearance, it is native to large parts of the U.S., and it is fully hardy in the North and into southern Canada. Z. (4)5-9
MAGMAC 12-18 in. - $24.95

Gossler Farm Nursery
http://www.gosslerfarms.com/catalog3.htm
MAGNOLIA MACROPHYLLA -What can we say more than this magnolia is the largest leafed native American tree. We have had young plants with 3 foot leaves. For those wishing to create the tropical garden, this is perfect and you don't have to dig it like many tropicals. M. macrophylla is hardy to at least -20¤F. (our tree thrived through -12¤F.). The flowers are also huge (up to 15" across and very white). 1 gal. $ 15.00

Sounds like a fun plant to grow. After a few seasons, people will be asking you about it!

Now the Kyushu hydrangea is suppose to get 8'h x 10'w according to one source. You can train it like a standard if it isn't already. I find a lot of variety in hydrangea sizes so far but will this provide the shade you are looking for? Are you looking for a wall effect or under the tree effect?

Here is a link that might be useful: Fairweather Gardens

They may be slow growing, but it seems some sort of Halesia or Styrax would be a small tree to provide Summer shade. I am sure the hanging flowers are beautiful and then a mess to clean up. I think M. macrophyla would need real shelter in order to avoid tattered leaves and can become a sizeable tree, as previously mentioned. Other are the black locust cultivar whose flowers are pink, instead of the usual white, and the red-flowered horsechestnut. And there are a number of other magnolias that do not become massive but would provide shade.

Oh, I gonna have to move that Magnolia for sure. I'll wait until next season; it's only a small sapling and I don't want to dig it up again and shock it. I would love to put it curbside but I don't think my neighborhood would be happy about the 3' leaves blowing all over the place. It wouldn't be protected there from the wind so it would likely make a mess.

Maybe I'll give it to mom and dad -- they have three or four acres (compared to my .125 acre) so there's room enough to grow a big beautiful tree like this.

I will look into Halesia and Styrax! I am not familiar with these trees, but I'd like something light and airy thst will filter very strong sun.

I put the hydrangea near the pool and it looks nice. I strategically place it right in the "Y" of a path -- left brings you to the pool ladder and right brings you to the gate for a veg garden.

BTW on the tree forum, someone posted that his magnolia grows 2' year. That doesn't sound slow growing to me???

PS Even when I do plant things I know, I often move them around... Ha! It's no wonder my back hurts!!! LOL

Frelinghuysen had a group planting of Magnolia tripelata. The leaves aren't 3' but they are big. I always collect a few with my kids which end up laying around my front porch. They always draw comments.