PGP's "Web of trust" doesn't actually scale and so it doesn't meaningfully improve upon just doing out-of-band verification with a handful of your closest peers and nothing for everybody else.
Web of trust can give an illusion of scaling because it uses sleight of hand to persuade you to accept transitivity of trust. If you see someone who took this seriously you'll find that almost all contacts show as "unverified" (when I've had PGP setups in the past that's what happened). If they just click blindly along accepting trust transitivity then everything is "verified" but based on trust beliefs that have no basis in reality.
The sleight of hand goes like this. You trust Alice. Alice says this is Bob and she trusts Bob. The correct inference is that this is indeed Bob (Alice says so and we trust her) but we still don't trust Bob. PGP tries hard to persuade you that you in fact now trust Bob. Bob says another contact is Carol, and he trusts Carol. The correct inference is null, we don't trust Bob so we don't care what Bob says. But PGP encourages us to accept that this is Carol and we should trust Carol too.
Web of trust can give an illusion of scaling because it uses sleight of hand to persuade you to accept transitivity of trust. If you see someone who took this seriously you'll find that almost all contacts show as "unverified" (when I've had PGP setups in the past that's what happened). If they just click blindly along accepting trust transitivity then everything is "verified" but based on trust beliefs that have no basis in reality.
The sleight of hand goes like this. You trust Alice. Alice says this is Bob and she trusts Bob. The correct inference is that this is indeed Bob (Alice says so and we trust her) but we still don't trust Bob. PGP tries hard to persuade you that you in fact now trust Bob. Bob says another contact is Carol, and he trusts Carol. The correct inference is null, we don't trust Bob so we don't care what Bob says. But PGP encourages us to accept that this is Carol and we should trust Carol too.