Try to run this test. If you query "what is my ip" in duckduckgo, or any of the other ones I mentioned, you will notice in the description of one of the top results this IP: 207.46.13.147. It's a BingBot IP [0]. It's a good enough test to spot where results are coming from.
Building even a mediocre search engine involves a gigantic index in >40 languages that is constantly refreshed, plus image and video indexes, porn, spam, malware filters, complex ranking, freshness, originality algorithms, constant quality analysis and continuous maintenance and improvements for the infrastructure. They are not transparent about breakdown of queries or details of their deals with Bing and Yandex. They try really hard to create an illusion that it is a real search engine, but seems like it is basically smoke and mirrors.
IIUC, they have built their own search, but use Bing(among others) for paid ads.
If this is the case, it seems that it’s the business model that needs innovation and not the search engine itself.