Fitzsimmons gave up 39lb to Jeffries. Langford only gave up 29lb to Johnson

The question you have to ask, is what was each man in terms of the division at the time?

Fitzsimmons was the reigning heavyweight champion when he fought Jeffries the first time, and clearly the best fighter in the world apart from Jeffries himself the second time.

When Langford fought Johnson he was a feared middleweight, but he was new to the heavyweight division, and not regarded as a great scalp yet.

I give Johnson a lot more credit for his wins over Sam McVea, who was regarded as major force in the heavyweight division.

I must also point out that Fitz might have weighed more than 167 when he fought Jeffries, and indeed Langford might have weighed more than 156 when he fought Johnson, though I have not seen any evidence in the latter case.

 

People tend to lump Johnsons wins over Langford, Jeanette, and McVea together, but they shouldn't.

Langford was only just testing out the waters at heavyweight.

Jeanette was green, but a significant figure in the squabble for the colored title.

McVea was seen by some, as the outstanding challenger for Jeffries title.

 

Langford had over 50 fights when he met Johnson, how many fights do you need before you," get better"?

 

Johnson was not an ATG heavy when he beat Langford was he? He had less fights that Sam under his belt.

 

Two more points to consider imo are that:
Fitz was 37 years old ,12 years older than Jeffries, and had been effectively retired for 2 years.