I think you didn’t chose the right ionic version in your topic, did you?!
Anyway, angular is for building web apps and cordova to transfer a web app in to a hybrid app. now which css or ui framework you want to use to design your app is up to you.
what ionic does is giving you a framework where UI design, cordova and angular are already in it. but you can still use ionic with bootstrap.
And i think the app shouldn’t look the same on all platforms. important is, that your app looks like an, let say, android app if you run it on android and the same app should look like an iOS app if you run it on ios. Which means that both versions could slightly look different on different platforms.
I’ve tried angular with onsenUI and angular JS with onsenUI and jQuery mobile and bootstrap and many other css frameworks but I had and have the best results with ionic. i’m very happy with ionic and would recommend it to you, obviously version 4.