Don’t forget about MIDI Bridge…This can sometimes be used when all else fails. I use it when I want to direct MIDI from my LPK25 to my Beatstep.
It can be used for simple routing or for complex processing of MIDI (e.g channel swapping or filtering)
At first it does not feel intuitive or easy to use but if you are experienced MIDI user you will find your way quite quickly.
I have been having same thoughts about why is it so difficult in iOS, but when i think back to when i started with PC, it was the same, nothing seemed to work consistently. There were lots of little utility apps that made life easier, over time the utilities got built into the Sequencers and DAW’s until they all pretty much offered the same functionality (being led by innovations at Steinberg e.g VST).
When you do get frustrated, please remember that in comparison to PC, iOS is still very young, and IAA even younger. As long as there is a demand for it, the same will happen with iOS as happened with PC. It will become more stable, more functional and in the end we will all wonder how we used to manage with a PC and the limitations it has (noise, size, lack of real portability, electricity bills). My first midi studio took up a whole room and I needed a power board with 12 mains sockets, I now have the same functionality as I had then in an iPad mini 8 inches by 5 inches, running silently (not even clicks from mouse buttons) on a battery.
Stay strong and keep the faith 