[donohoe]

>> Extending it without plugins, many of which are paid, is a nightmare.

Many of are free, and you can often build your own. You can easily extend it without plugins, but you're doing your future self a favor if you stuck your new features in one (so you can update themes etc easily in the future).

>> Adding custom fields is laborious, configuring post type display modes is a slog as well.

Hard disagree here. Whether you are using ACF for custom fields or post types, doing it manually takes more time but is not that difficult. Its typically a set of actions you wouldn't do often either.