Mergers and acquisitions are a part of business. In the Telecom industry they've been going on at a fever pace since the 1990's.
The results for some deals work out better than others. I'd say that T-Mobile has done well acquiring Sprints valuable network (massive amount of 5g spectrum) and large customer base.
That has allowed T-Mobile to rapidly build out its nationwide 5g network and leapfrog AT&T to become the second largest Wireless carrier in the U.S.
Unfortunately for employees when you merge two nearly identical companies there is redundancy in operations. Business by definition seeks to maximize shareholder return not employment opportunities. Therefore overlapping job functions are eliminated over time. In this case, it's been well over 3 years since T-Mobile and Sprint merged.