At least for Samsung S7 it is not possible to use DJI Go if none of apps is set as default for USB.
I always put samsung to flight mode to stop it linking / responding to other inputs. Two flights this weekend went well with no disconnects. I still think iPhone works better...as my friends use when flying my msz.
Interesting... works fine on all Samsung products I've used. That feature was more apparent in newer OS versions, are you running 8 or 9 (actually 8 is last supported version for S7), the S7 started with version 6 and this feature wasn't as apparent. If I recall correctly in earlier versions, you did have a default app but you could easily select other apps to run instead, or place as new default.
I've ran multiple flight apps on Samsung products since version 4 KitKat upwards; Note 4 & Tablets without issue.
It's really not an issue of Hardware OS, Android has many products and the majority are lower end devices... the upper end devices that are more comparable to Apple hardware will perform well. Heat issues exist for ALL devices, all will fail on hot sunny days near the same temp, a new iPhone & Samsung will both present a heat failure message within the same amount of time when exposed to heat, I personally experienced it a few times simply leaving in a car a bit too long.
I will agree, Apple doesn't offer lower cost / lower scale hardware, they only offer upper end hardware. When compared to Android hardware. A lot of Android hardware is 30-60% less cost, that indirectly equates to quality of components. Lower grade hardware quality gives the perception Apple runs better... false, upper end hardware all runs about the same. The older iPads won't provide the same service or performance either, some apps specify only the newer iPads as minimum requirement.
But... if a person enjoys their Apple or Android, likes the brand or OS design that's a happy person!