First, sorry to see your previous starter effort didn't work out well. Since we don't have the details on the process you were following at the time, it would be difficult to decipher where it got into trouble. If you ever want to give it another try, you might want to see [ Anonymized URL Blocked ] that could help you along; I'd also be happy to answer any questions there if you need help.
But you are more specifically asking about Ischia vs home made so let's get to that.
The cool aspect to getting a pre-built starter like Ischia (or any other dried starter) is that all that cultivating work has already been done and the specific yeast & lacto are already settled in, they just need rehydrating to take over the soup again. Even though you are adding your own flour which has traces of it's own set of critters, the existing guys are there in large enough quantities that they can easily overtake any weaker new cultures and remain the "kings of the hill".
This is where you get into the famed "Can you really maintain a specific culture or will your local guys eventually take over?" heated debates, which is an entire other topic of it's own.
Can you get the same properties as Ischia in your own homebuilt starter? There's a possibility you can - as Bill noted already, somebody somewhere obviously did - but there's also a possibility you will not. Ischia has been noted as having the qualities people like and look for in pizza. Some of those qualities can maybe be drawn out of the yeast/lacto that you cultivate in your own starter by manipulating temperature and time, feeding cycles, flour type, etc. But it may be a lot of trouble to go to and you might not end up with the specifics that you'd have available with a well kept Ischia. It is, in other words, a handy shortcut to the desired set of qualities people look for in pizza.
Your own starter could still be great for making really tasty bread, however. If you decide to give home made starter another go, you wouldn't be the only person who keeps one starter specifically for pizza and another for bread.
Hope this helped!