A few things here.
The Epic Prox 51 has a screen resolution of 454x454 (not 545x545 as claimed) and has a diameter of of 35.56mm. This gives it a screen area of 1018mm2.
The Apple Watch Ultra has a screen resolution of 502x410, and has a diagonal size of 49mm. This gives it a screen area of approximately 2400mm2, over double. The area is larger because square vs circle.
The Epic Pro 51 has an AMOLED screen with 1000 nit peak brightness.
The Apple Watch Ultra has a LTPO OLED with 2000 nit peak brightness.
Garmin do not publish the refresh rate of the Epix 2 screen, but it's quite clearly below the 60hz that the AW Ultra is running at too - which is why it's not as smooth looking.
The Apple Watch has a much larger screen, a higher resolution screen, and a higher brightness. Additionally, if you check your battery usage stats on an iPhone or watch (or better still - use Xcode when building an app), you'll find the screen is a large portion of the battery usage figures.
I love Garmins. They're amazing devices. But if you value screens, then it falls short of the AW Ultra.