The 'Legitimate' way of extending a Fiori App ?

A hello to everyone,

          We (The Developers) are often presented with requirements to extend Fiori Apps to meet the actual requirement. Of-course it isn't rocket science. But what exactly is the correct way to drive a rocket is not what i have been able to understand. Let me take this from the Gateway extension perspective. Done asking seniors on how do i extend a Fiori Application from Gateway side. I get the below two answers.

1. Hey, why don't you try implementing the BADI mentioned on the SAP Help Page.
2. That's too much work .... rather write your code in DPC_EXT and move on.

           As a developer, relatively new to Fiori. What's the correct way to progress ? Yes, there are situations where implementing BADI is the only possible way (For example the Wave1 Apps (i guess) which were designed through the SE80 method and one can't simply open them in SEGW). But apart from that is there any 'standard' approach that SAP recommends upon following. Request you all to include reasons for insisting upon following a particular method for extension of the Odata service.

Thanks,

Vaibhav Deorukhkar