Au contraire. I would argue that the metadata story is stronger with links. In Kinetic, at least the last time I looked, you could only automatically add meta data from the table that you’re attaching to (so no customer name or ID for quotes or order for example). Again, the last time I checked in SharePoint attachments, all of the documents go into one Document Library. This means all documents share the same meta data. 
If you create Document Types in ECM or SharePoint and use links, you can have many Document Types with only the meta data required for those document types. You can have multiple SP libraries with their own security and retention policies. ECM has very strong meta data, security, and retention capabilities and is integrated with Kinetic very tightly.
To my knowledge, Kinetic doesn’t store any meta data. It only prompts for it during the upload and lets the repository store it. If you capture it during the browser upload too, then what’s the difference? 