I don't know if it even was the best tactics anyway. Ok, in the end the result was the best possible. But if Alaphilipe just sprinted normal, Roglic would have been 4th most likely. Even after the work, Dumoulin was still very close at the top of the RaF. Maybe without working they could have been with 2 in the elite group (although Dumouling probaly is just not explosife enough for this). Or they could have made the race harder for exemple on laRedoute, or even earlier in the race, tiring Alaphilipe's legs, to prevent his famous attack in the last 500m of the final climb of the race. In this way Tom was just preparing Alaphilipe's jump. Roglic normally was without a chance in that sprint.