Hello there!
I too would advise you to stick with your Swan and Dolphin reservation.
My teens (now 17 and 15) love that resort area - they can walk or ride a boat to two of the parks (Epcot and Hollywood Studios), they can walk to several restaurants (some are closed due to COVID, but I have hope more will reopen before July - we have a trip 1-5 July! my son really loves the ESPN Zone restaurant) and there used to be entertainment - jugglers, etc - on the Boardwalk pre-COVID (again, hoping this will return - but sadly, know it might not).
If you're a Marriott rewards member, I think you can earn points at the Swan and Dolphin as well? (I might be wrong about the hotel brand.) I know everyone has their opinion on whether the Disney resorts/ on property hotels are worth it or not, but I think being so close to two parks and being in the Disney 'bubble' will really be worth any extra dollars you spend. I love sitting by the pool in the afternoon with my spouse, while my kids can walk back to a park or go get a snack and then we can all meet up in an hour or two for dinner or park time or whatever. Sometimes my husband goes back to a park with just one kid and the other one hangs out with me or vice versa. The possibilities are open when you stay onsite and have multiple transportation options and things located close by. When we stay offsite, one of us would have to drive one kid to get a meal or take the kids back to the park (which usually meant we'd just have to go back with them), etc. Now, the 17 year old would want to drive himself, but that would leave us without a car - you get the idea - I find offsite a lot less relaxing due to the logistics.