I just really disagree with you here. You're mentioning the Red Sox getting some good postseason performances from randos but that's not the comparison I'm making (obviously, since the Yankees haven't had a postseason yet). The Red Sox had a BUNCH of lousy players who played lousily, as you've pointed out, and it sort of baffles me to this day that they won 108 games.
Here are some of the guys the Yankees have:
-Nestor Cortes, formerly DFA'd, now in the conversation for the Cy Young
-Jose Trevino, career high of 0.6 fWAR, currently at 2.4 and on the All-Star team
-Matt Freaking Carpenter, who's OPS the last four seasons has gone .726, .639, .580, 1.251 1.306 now
-Marwin Gonzalez - Marwin Gonzalez! - has a 103 wRC+ and 0.7 WAR. Do you remember that guy when he was on *our* team?
-Clay Holmes, a nothing of a prospect and a nobody in Pittsburgh, has an 0.46 ERA and 1.5 WAR in 39 innings
Seriously, look at the Red Sox' stats from 2018. I'll give you Steve Pearce (though he only played in 50 games). Beyond that everyone who was really good for them was either a major star or a young blue chipper. In fact, a couple of their stars had negative WAR, in Hanley and Pedroia. You mentioned Johnson and Velazquez but those guys had ERAs in the 4s and worse peripherals; nothing like, say, Nestor Cortes, who has legitimately pitched great.
The Red Sox ended 2018 with 13 players in negative WAR territory; the Yankees currently have 1.
And then there's the fact that the guys on the Yankees who aren't journeymen are almost all playing at the top of any reasonable expectation. Rizzo, on a downward trajectory since 2019, is somehow back at his peak level of offensive performance. Taillon and Severino, with I believe 3 Tommy Johns between them, have somehow been healthy and effective all season (well, until tonight).
Anyways, if there's an upshot to all this, it's that they can't keep this up. Like, Matt Carpenter is not going to end the season with a 1.200 OPS...
ADD: Here's another way to make the comparison: the Red Sox had 15 players contribute 1 fWAR or more. The Yankees already have 16 barely halfway through the season.