As I said ESPN and ESPN+ are actually different services. You can, as you have done, subscribe to ESPN+ without having access to ESPN programming but you cannot get ESPN programing without a TV subscription. Even though ESPN shows the content together on a lot of screens they are actually two separate services.
However you do NOT need a CATV subscription to access ESPN content. A subscription to Sling which I think starts at $15.00/month (The Orange tier is what has ESPN I think) will provide full access to the ESPN content but not to ESPN+ which is still separate.
To get access to ESPN content and ESPN+ content you must have two separate subscriptions. For me it is wel worth it. In fact I subscribe to Sling Orange and Sling Blue with their sports add on because I want ESPN and ESPN+ and Fox (FS1 and FS2) and NBCsN (For the EPL) content. The total cost for me is somewhere in the vicinity of $55.00/month for all the sports I could ever want. Of course everyone must make their own decisions about value vs cost but for me it is really good value.
BTW: I actually access Sling via my Fire TV rather than my Roku. I find the Fire's interface for Sling MUCH better than Roku's. Plus the FF and RW often does not work correctly on the Roku. But I use the Roku for ESPN content because the ESPN app is better, for me, on the Roku.
If ESPN+ increases its price even just a few dollars I may well drop it. I sub to ESPN+ primarily for the MLS and the level of play in the MLS has become so poor that it is often painful to watch and my primary use of ESPN+ is for MLS content.
Two Roku Ultras, three Roku 3s and a Roku 1
"Part of the secret of success in life is to eat what you like and let the food fight it out inside." Mark Twain
Van Roy's Law: An unbreakable toy is useful for breaking other toys.