There's no reason a service(s) couldn't coexist alongside or within a network of individuals. Said services could even recruit contributors from the wider network, or make a service out of "verifying" and storing network events that they deem "accurate", on their own relays. The 2 things would help create accountability for both.

But at that point, that service needs to render and download the page. Then they need to compare it to the page downloaded by the user. You can't use a comparison operator or anything because on most pages, it will vary based on the user and device. You would need manual review and judgement calls by the reviewer which will have to check word by word to see if anything is removed or added, then for display they will have to decide if differences in presentation are valid or not. Basically, checking a page uploaded by another user is far more laborious and complex than just capturing it yourself. The far more likely scenario if this is implemented is, there will not be a separate service verifying pages uploaded by global users, but those services will be the ones capturing and uploading the sites. So the user will still just tell these guys a link for them to screenshot, but there will be multiple competing services that the user can choose from, and they will all be interoperable from multiple clients. While any npub can post a capture, all the clients will curate the captures based on the trustability of the npub and your captures won't be used for anything but curious people looking up shit for reference. Most clients will work on a fully whitelist basis, only showing captures from a few selected npubs, banning them at the first sign of forgery. This is still better than the internet archive, but you will never see crowdsourced web captures that are worth shit to anyone.