Since Botvinnik didn't even manage to win a single WC-match outright as a defending champion against four different Soviet opponents, that may very well be true.
The problem is that Fischer didn't even come close to qualifying to such a match.

Fischer v THE SOVIET UNION

you're treating this like a classical game.

You dont say

No internet. CHECK
No database. CHECK
No engines. CHECK
Bobby Fischer present. CHECK

We actually do.
<Each player had five minutes for the whole game, the usual time-limit for blitz before the introduction of electronic clocks.> https://en.chessbase.com/post/the-b...

And for the avoidance of doubt, as they say, if that match had been played in 1970, then yeah, Fischer would have crushed Botvinnik.

Bobby crushed the Soviet School of Chess.

Efim Geller beat Robert James Fischer 5 to 2, with 2 draws

I doubt it, even though after 45.Kd6 Stockfish 11 indicates that White has a mate in 20. Depending on his remaining time (there were no increments in those days), Tal could have easily missed the winning moves along the way. He might even have lost as he did in the game or on time. Because, as you said, that's blitz.

Bobby beat the corrupt cheatin Commie Soviet School of Chess ... on his own.

I think the reality is that today’s players are the best ever, and that a guy like MVL is better than any of the previous champs before Carlsen. The metric I am looking at, however, is a player’s skill compared to their peers. It’s hard to argue that Fischer wasn’t the farthest above his contemporaries. YMMV

2) Young Fischer won the 1962 Stockholm Interzonal by the absurd score of 18.5 out of 23. This would stand as qualification to play a match against Botvinnik or anyone else. Moreover, according to ChessMetrics, Fischer reached number 1 in the world in 1964.

I think it is pretty reasonable to say that Fischer singlehandedly defeated the soviet chess machine, and pretty convincingly at that.

<I think it is pretty reasonable to say that Fischer singlehandedly defeated the soviet chess machine, and pretty convincingly at that.> Fischer was definitely the worlds strongest player between 1970 and 1972. No one is denying that.
Please build your straw men with greater care.

after 1972 Karpov is the new soviet in his prime and Fischer turned tail and ran. It's that simple.

I didn’t realize that <Harry> meant to claim that Bobby dominated the Russians before 1970. If that’s what he meant, he is exaggerating, and I will stand down. That said, from age 23 until his death, Fischer won EVERY tournament or match he competed in, with the exception of the Interzonal he withdrew from while leading, which is sort of like dominating.

The jury is still out if he's a basket case or some kind of reclusive genius. What the world has come to some kind of consensus on, is that his views on Robert James Fischer is, to put it mildly, a bit over the top.

Gaito:

click for larger view

White to move

In this ending White has an elementary win: 43.Ke5! Rxh2 43.Kd6 Re2 44.Rc5 a4 45.Rc3, and Black could resign. Instead, threre followed 43.h4?!, a move that still wins, but his task is made more difficult. The game went 43...a4 44.Ke5 a3 45.d6?? (Amazing! 45.Kd6 is an elementary win) Re2+ 46.Kf5?? (46.Kd5 draws easily) 46...Rf2+?? (now it was Fischer's turn to blunder. 46...a2 wins outright) 47.Kg4 a2 48.d7?? (Was Tal drunk or what? 48.e7+ is a clear draw.) 48...Ke7, and Black finally won.

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