Scotland were bounced out at the group stage.
Collins told BBC Sport: "Three centre-halves on the pitch in a game we have to win means we have less creative players at the top of the pitch.
"You've got to have overloads. There were no penetrating passes from midfield, nobody making any runs in behind, the whole tournament. The only way to change that was to change the system. We never got to the byeline in the whole tournament, for cutbacks.
"In fairness to the manager, his system worked in the qualifiers. If you've got a big striker at the top of the pitch, it means your wing-backs 20, 30 yards from the byeline can put balls in the box because they see you've got a big centre forward, who's going to get flick-ons, going to create knockdowns for (Scott) McTominay coming in late. We never had that.
"When you've not got a tall striker, you've got a smaller striker, you've got to be more precise, you've got to try and get to the byeline for cutbacks for him. He was left up there on his own.
"A lot of fans have criticised Che Adams. He had no service and he was asked to work the full width of the pitch. He had no energy after an hour because he had done so much work for the team.
"Against Switzerland, against Hungary, we should've gone 4-3-3. Games you've got to win, you've got to have players further up the pitch and stretching opponents' back four."