I spent 20 years working as a sys admin, moving to new offices around the globe every few years. No matter which country I worked in, every single sys admin I’ve ever worked with always pronounced it “sequel.” I’ve never met anyone in real life who spelled out the letters when speaking it.
It’s always been an otomotopoea (really fucked the spelling on that) to me. Like, the sound of someone sliding a can across the floor and into a bell. Sluuuuurrrrrrrrrr pink