With Angular templates, there's an entire new language, with its own weird syntax ngIf/else, ngSwitchDefault, let-*, pipes and other components that get pulled in based on whether you forgot to set up correctly or not in modules far-far away somewhere in the codebase, brackets of different sorts having different functions and just a lot more stuff to remember. And if it doesn't work, you're gonna get a silent error most of the time with no easy way to set a breakpoint to investigate.
I also don't believe there's any real separation between the HTML templates and the Component class, just because they're written in separate files. They're just as tightly coupled as any regular React component, just harder to follow. I don't think I've ever seen an Angular component, where you could swap out the template, without making simultaneous changes to the Component to accommodate it, which should be possible if they were truly separate.