Did Tuchel's subs lose us the game? Well, he said he reacted to Argentina getting the upper hand. Match stats show (after conceding in min 55) ARG had dominance in every minute following. Tuchel didn't react until 72' - taking off Gordon.
The later substitutions were all defenders or like-for-like.
Did Tuchel tell the players to sit back and defend? I've seen no evidence.
Did they
decide to sit back? Well perhaps subconsciously; but in reality it will be a response to more aggresive play by the World Champions, and an aggregation of many small decisions (tracking back when they could have stayed upfield, playing a safe clearance instead of trying to start a move, etc ... )
https://www.bbc.co.uk/sport/football/live/c77yp11e4r6t#MatchStats
The substitutions:
Number
18, Gordon,
Attacking Midfielder
A. Gordon
E. Konsa
72'
4, Rice, Defensive Midfielder
D. Rice
N. O'Reilly 82'
, substituted for N. O'Reilly
[midfielder/full-back - Matt] at 82 minutes
24, James, Defender
R. James
D. Burn 82'
, substituted for D. Burn at 82 minutes
25, Spence, Defender
D. Spence
, substituted for M. Rashford at 96 minutes
5, Stones, Defender
J. Stones
, substituted for I. Toney at 96 minutes