I'm still seeing very slow Affinity Photo (latest app store version) initial launch times on Big Sur 11.2.1. Here are my timings on a 27" Retina 5k iMac (Late 2015) with 4GHz i7 processor, 32GB RAM and 512GB SSD:
Affinity Photo: 22 seconds Adobe Photoshop: 10 seconds
Second launch is definitely faster:
Affinity Photo: 3.0 seconds Adobe Photoshop: 2.5 seconds
But since I don't use either app frequently, the initial load time is what's most noticable. So when I need to open one for quick bitmap editing, I choose Photoshop since it loads so much faster. Twenty-two seconds feels like an eternity with Affinity Photo. Yeah, I know, first-world problems! 😜