Correct. I would not waste my time trying to reserve and wait for a UberBlack or XL; the chance of getting one to accept and actually show up is slim to none. Assuming you can find a luggage cart (way better odds than getting an Uber), the walk from T3 to T7 via East Way is, while not pleasant, doable in about 20-25 minutes (normally 10 minutes with minimal luggage - I’ve done it from T1 to T6). If you want to take the safer route of walking the horseshoe sidewalk, that would normally take about 20 minutes with minimal luggage, so add maybe another 10 minutes with a cart. The inter-terminal bus would probably be pretty similar in time. Use GoogleEarth street view to familiarize yourself with the route. Bottom line, your connection of 2+ hours is very doable but won’t be pleasant.