Will using my own router resolve some issues with the T-mobile router?

I have had T-Mobile home internet for 2 years. My kids got me the new Philips Hues lights for outdoor fun. I have 22 devices hooked up with two ethernet cables, one for a business computer and the other one is for these Hues lights. All the sudden my router stopped working. The speed dropped to a quarter of what it was. I was getting major buffering. Nothing was working so I called and the sales rep size well you're only supposed to get between 25 and 125 and I says you're advertising around 250-300 download speed it's like where did you see that so I had to show him that. Then I purchased a TP-Link Archer AX21 . I download speed now is between 350 and 400 The two ethernet ports work perfectly. Nothing's buffering. It was well worth the money. I was almost worried that I had to go back to spectrum and luckily this work now I love T-Mobile works great