The differences are not close ones, so this is a short list.
You do not need a consent banner for Skomi. Nothing is stored on your visitors' devices by default. Identity is worked out at our end from a value that is thrown away every day. GA4 stores identifiers, which is what puts the banner on your site, and a banner is not free: every visitor who declines is a visitor you stop counting.
Every visit is counted, at any size. Google's own documentation puts the limit on an exploration at 10 million events for a standard property; past that it samples and scales the result up. Standard reports are not sampled, so this bites when you start asking the more interesting questions rather than when you read the dashboard. Skomi keeps the rows and adds them up, however many there are.
It is one product, not a platform. GA4 can answer more questions than Skomi. It also takes longer to learn than most people are willing to spend, and most of that surface exists to serve advertising you may not be buying.
Your apps are in the same place as your sites. Both do apps; in Skomi they sit beside your sites under one account, with heatmaps, session recordings and a feedback board on the same data.