I do believe that to use the C3 runtime you need at least IOS 12. The C2 runtime can run on IOS 11.
This per construct.net/en/blogs/construct-official-blog-1/launching-the-new-construct-3-runtime-1048
If you're trying to use a Gen 1 iPad, I'd give it up, Safari only goes to 5 there, and apps are few and far between.
Since IOS adoption rates are quite high, I'd target later devices. It will simplify frame rate issues etc and enable you to push the envelope further than if you cater to very old tech.