I definitely pick Marshall in my all time XI, but I think it's fair to say that the idea of him being a consensus "locked-in" pick for such a team has become more and more prevalent in recent decades.
At or around the turn of the century, give or take, I saw all time XIs selected by Peter Baxter, Christopher Martin-Jenkins, Henry Blofeld, Bill Frindall, Jonathan Agnew, Don Bradman, Richie Benaud and Ashley Mallett, and Marshall didn't make any of them.
TMS chose their 40th anniversary team for 1957-1997 and Marshall didn't make that team either.
And if the all time rankings of John Woodcock and Nick Brownlee around that time were converted into all time XIs then Marshall misses both those teams too, and by a long way.
To repeat, I disagree with all of these, but the idea that Marshall is a near-universal lock in an all time XI certainly wasn't the case until relatively recently.
So I want to look at this from several perspectives....
First up you referenced "locked in", even as I illustrated in the post. I have Bradman and Sobers by themselves.
Then Marshall, Hobbs and Tendulkar, a gap then Warne and Gilly.
What does Bradman and Sobers have? Well the numbers, an unchallenged label as best as what they did and a legacy.
Marshall, Hobbs and Tendulkar, have the numbers, and are unchallenged as among the 3 or so best to have ever done it, and they all have the peer rating. All they lack is the legacy of the first two, though Hobbs is pretty close. But why don't they, because they haven't been retired long enough?
I also look at it from this perspective. If you are selecting same side for a WT championship, Sobers and Bradman are either off the table or already selected, who's next?
In any event I went though the names and teams you provided. Woodcock and TMS I'm familiar with.
I could find nothing for Peter Baxter and Gemini said there's no evidence that he made one.
I've read CMJ's rankings and Marshall is no. 11 and the 2nd fast bowler I believe.
Henry Blofeld, his team was interesting.
Bradman | Hobbs | Sobers | Richards | Lloyd | Botham | Knott | Warne | Trueman | Spofforth | Laker
Again I can't find anything for Bill Frindall,.or Jonathan Agnew neither could the AI. Not saying they didn't, just couldn't find anything. Was probably rolled into the TMS effort.
Bradman, ahh the one that opens with Barry and an attack of Lindwall, Lillee, Grimmett, Warne and Bedser. But again, he opens with Barry so I'll allow it.
Ashley Mallet also named a test XI, and from what I've seen Marshall does make it. Along with Lillee, Warne and Grimmett.
Benaud openly said his team wasn't the best and his views of the WI attack were well known and hypocritical as hell.
Now I'm not saying that Marshall has appeared in every team since he retired, but more than not and often the credible ones.
Even Swanton in '91 named him to his all time XI, so it wasn't purely just at the turn of the century.
So even if Bradman and Sobers alone holds a place in the highest of pantheons in this (and all) regard, theses nothing wrong with having Marshall, Hobbs and Tendulkar right behind. Warne and Gilly as well deserving mention.
For my personal views, of the 7 or 8 guys even in this conversation, if I'm only getting 2 picks, I know who they are, probably the same for everyone, if it's only 3, I know who I'm selecting if we're picking a team to save a planet.
So yeah, these guys are locks for me. Prescedence, numbers, impact, peer rep, and guys who have claim to the title as best.
Everyone is free to disagree.