You are right that it's not apples to apples to compare Jacobs' pre-draft projected draft capital to Guice's actual draft capital, but that's all the information we have to work with right now. How people projected the NFL felt about Guice leading up to the draft isn't really relevant to me anymore because we now know how they actually felt about him. We don't know that yet about Jacobs so the things we've been hearing and the places he's been mocked are all we have to work with. You are correct that if Jacobs falls to the late 2nd things change a lot and it may end up being presumptive of me to already be calling him a late 1st/early 2nd round pick.
You already mentioned it somewhat in terms of the reasons Guice dropped possibly being dubious but personally I don't really buy Guice's slide being because he played too much Fortnite or whatever the story of the day was. The strong draft class is also less of an excuse for me because it's not just that he landed in the late 2nd, it's what teams did to avoid him. The Lions had the fewest picks in the draft but still traded one of them away to move up and grab a relatively mediocre prospect in Kerryon Johnson when they could have just stood pat and gotten Guice.
I do still like Guice, but I think it's fair to treat him as a mid-2nd roundish type prospect and not the mid-1st type guy we all thought he was in March of last year. If Jacobs slides similarly, it will be fair to call him that as well.
I've seen a lot of people say this, but it's worth noting that Peterson's production dropped off pretty precipitously after the Alex Smith injury, and they'll be without Smith again this year.
With Smith (10 games):
171-723, 7 TD, 4.2ypc
14 rec, 168yds
14.51 fantasy ppg
Without Smith (6 games):
80-319, 1 TD, 3.9ypc
5 rec, 40yds
7.8 fantasy ppg
That's fair, and if Jacobs does indeed get drafted where he's being projected he will be an interesting experiment in the disparity between measurables/production and what scouts are telling us they are seeing on tape.
Still, even more than measurables and college usage are indicators with correlation to success, we all know the #1 indicator is draft capital so if Jacobs is in fact liked enough by teams to go ~30 picks ahead of where Guice went then that is very notable.
Would they? I'm certain using last year's March evaluation of Guice people would prefer him. But would the NFL? It was a strong class but it's not like Kerryon Johnson was some great prospect (it seems like the NFL likes Jacobs a lot more than they liked Kerryon as a prospect) and he went ahead of Guice.