I don't think that it matters much at all if Pogacar takes yellow earlier in the race. It is only tradition which says that his team must work, nothing more. For example, if he takes yellow and a dangerous break gets away, and it looks like a second tier GC rider is going to be in yellow by five minutes, so be it. Remember that Jumbo - if in this scenario Roglic is 30 seconds behind Pogocar - are losing just as much as UAE; the chance to wear yellow into Paris. Also, when Adam "I'm not going for GC" Yates was actually in yellow, what happened for much of the time? Oh yeah, Jumbo did most of the work anyway (or Bora).
Pogacar was understood to be a serious contender. If he’s in yellow early, and he’s isolated on every stage he has an enormous target on his back and he will face an endless succession of riders trying to get up the road. He can’t mark them all and he can’t rely on Jumbo to do it in the same way they did for Roglic. In fact Dumoulin would be the likeliest candidate to go on every stage.