Hi Kely,
the answer will be highly dependent on your own content needs. Yes, You’ll be able to stream a huge amount of content with the AppleTV box. As an example I’ll give you my own setup: I have AppleTV+ through my AppleOne subscription, I have Amazon Prime through a temporary Prime subscription. The YouTube app provides a lot of ad supported content (no charge but you’ll watch ads), I have PlutoTV and Tubi which both provide significant amount of content that is ad supported (no charge but you’ll watch ads). I have CuriosityStream for 1 year at 20$. And due to my HOA, I am captive to a minimum Spectrum subscription. But I do not pay for a cable box, I get the subscribed channels through the spectrum app on AppleTV (Fyi, I believe Spectrum offers a substantially lower cost option for steaming a handful of channels if you subscribe to their broadband offering) (Important side consideration, a cabletv box with DVR is typically an energy hog.. I saw a test done that showed a 7 to 9 dollar monthly electricity bill for the device). For myself I have a very huge amount of content to choose from and I’m substantially below what I see for most cable pricing. Also note, if you are in an urban or nit too far from an urban area you can get a relatively cheap HD antenna that will provide a surprising number of broadcast channels.
However, without a “cable” DVR box, the DVR options are in cloud only and will add extra cost. IME it is good but it isn’t as good as the physical dvr box. So If you DVR a lot of shows and like to skip all commercials without fail, the DVR cable box is tough to beat. Also, cable will typically provide a number of live channels together in one place. That is tough to replicate through a non cable app. Nite, the AppleTV app does give you a one app place to subscribe(pay) and view quite a lot of content providers but it will not replicate cable.
So this will be your choice as to what is best for you. You can both running simultaneously fir a short bit to see if one or the other platform will work for you. I’d consider writing down what channels on cable you really want to have, put down all costs associated with that cable bill, then research the subscription cost to view those channels via an app.
I’d also relay this last experience: cabletv and box is a very familiar way and user experience to provide content. We tend to be comfortable with this known commodity and operation. But it takes just a few weeks to adapt to a new way and user experience of streaming all content - though noting that much of which won’t be “live”. After a few weeks the huge amount of content offered via AppleTV box and the apps you install on it becomes the new and comfortable way/user experience. That break in period will be necessary but it will segue that comfort level to the new content platform delivery and user experience.