As far as I know Inbox bundles are a unique feature and one I could not do without.
Folders and filtering rules never worked for me because they gave me multiple "to do" lists. It's vital for managing complexity to have a single queue to work through. If you want to use your inbox for that - then traditional email clients fall short.
If something is filtered out of my inbox then I usually end up forgetting about it. If I can't group things in my inbox then it becomes overwhelming.
- The mobile app arbitrarily doesn't allow labelling something and keeping it in the inbox.
- It puts emails in the inbox under a folder when labelled by a filter, which usually ends obscuring important messages.
- It doesn't have something equivalent to inbox sections (I use the crap out of these as my inbox has multiple different streams of things to action in it from multiple email aliases - personal, business, opensource, travel, bills, etc).
- As others have mentioned, Inbox is not very information dense.
Google sure had a challenge updating Gmail, since there's so many people using it in different ways. It'd be really interesting to see their top usage patterns summarised.