In other words: a VPN service can't by itself solve all problems which potentially lead to deanonymization, it can only provide anonymous networking.

Why can't it aim to solve what it can do? TOR is a great example: the TOR network itself can't perfectly anonymize you due to browser fingerprinting, but users of the TOR Browser get both the TOR network resisting deanonymization on a network level and a browser with plenty of anti-fingerprinting measures built in. A VPN could aim to prevent deanonymization on a network level so that users who want to stay anonymous can use the VPN in combination with fingerprinting-resistant software.