-Coupled to OS updates, meaning that people on older versions of the OS will also have an older browser, with worse standards support (thankfully apples upgrade policies aren't as bad as android manufacturers, or this would be way worse)
-lagging behind on standard features with less frequent, big updates that still often end up missing crucial things (my prime example is how long it took them to support webp, which they thankfully finally support now, but there's plenty of others)