I bought a Lexar 4Tb SSD with a uGreen enclosure.What external drive did you buy? All the USB cables look the same, it's horrible for high performance needs if you plug one in that's too slow for the drive... I use an external Samsung 990 Pro in an NVME enclosure and it's blazing fast. Those "experts" tend to just be Apple haters for their pricing models, a lot of real experts on performance have measured the internal SSDs and there can be good perf improvement by having larger SSDs simply because the read/write rates are higher...
I returned my mini as the 1Tb that I figured I needed wasn’t enough and spent a lot of time simply managing storage. To me, I felt getting an internal SSD was a Better solution, however, after I returned the mini m4 pro, apple announced the new M4 Studio…so I ordered it immediately…with a 4K internal. While the mini ran so hot I had to buy a fan, even under intense use, the Mac Studio is cold. The larger size enables a much more efficient cooling system. As it’s a desk-top, that suits me fine.I got my M4 Mac mini Pro with an internal 2tb SSD. I based that decision on MY needs as well as performance. I was willing to pay the extra price. It makes the transition using migration assistance so much easier when going from the old Mac to the new one since the old Mac had a 2 tb SSD as well. It was seamless . I complement that SSD with an external SSD, the same Samsung 99O pro. 2 tb. SSD that you purchased. I then copied my Apple Photos library over to the external drive.
I kept the external SSD as it’s useful as backup storage when we’re away and shooting a lot of images.