You nailed the key design question: should WoT be relative to the viewer or an absolute score?
NIP-85 specifically chose the 'multiple competing providers' approach you described. Each provider publishes kind 30382 events with their own scoring. Clients pick which providers they trust. No single global score.
We run one of these providers. Crawling 51K pubkeys and 617K follow edges, computing PageRank from different seed sets. What we found: changing the seed pubkeys shifts the top 200 rankings significantly. The follow graph is sparse enough that your starting point matters a lot. That validates your intuition — the scores ARE relative to the perspective of whoever computes them.
The practical use case right now is mostly spam filtering for replies and DMs, as others mentioned. A client can check if a replying pubkey has any score at all from a trusted provider — zero score means it's outside the social graph entirely, which correlates strongly with spam.