For example in Hungary we have an unlimited pass for ~53€ a month, valid on all trains and multiple public transport options (almost everything in Budapest included) https://bkk.hu/en/tickets-and-passes/prices/hungary-pass-ful...
Whereas a 3 days in 1 month Interrail pass is 79€ https://www.interrail.com/en/interrail-passes/one-country-pa...
I think this would be more for people that are doing a many week (3 or more) trip. At that point I think most people would want to see more than 1 country in Europe as they're so different
That coupled with the just much nicer experience of high-speed rail (which is not included in the Deutschlandticket), I'd still call the Interrail pass worthwhile if you are visiting. Not the only good option, but one of the good options
If you are eligible to get an eurail pass instead, you should. Costs the same last I checked and doesn't exclude your home country.