The map doesn't make complete sense on its own terms - how and where is the threat from south of the Loire to come from, and be supplied?
In reverse order...
Where were the German 1st & 19th Armies supplied from through August? Hint, there were two army & a army group HQ in south & western France, with supplies stocked for two Pz Corps & two infantry armies.
As of 1 Sept German Army Group G appears to have five field or mobile infantry divisions to deploy northward, & the 11 Pz Div. There were another five static & training divisions to leave behind. In theory a infantry division or two from the Ligurian Army could be transfered to AG G. Its not difficult since the railway link between Italy & the Rhone valley is still usable.
Facing the US 3rd Army 1 Sept were the 3rd & 15th PzGr Div, two field Inf Div, & assorted regiment/brigade size units.
I dont have the precise distribution for the German formations that appeared along the Rhine 1 - 15 September. It looks like a total of eight Inf Div & seven Pz Brigades crossed to reinforce the western defense. Another six Inf Div appeared from 16 - 30 September. If 33% of these reinforced the defense south of Trier then five Inf Div & a couple of the armored brigades are added to those present in the Lorraine region 1 Sept.
It looks like 3rd Army had two armored + four infantry divisions, and 3 armored cavalry groups. This looks strong, but it appears only two divisions reinforced the 3rd Army during Sept, the 79th ID & Fr 2d Armored. & there is the question of supplying the extra corps.
So, as Sept progresses the US 3rd Army finds itself fighting in two directions, with eight divisions or nine if the aggregate AC Groups are counted as a division. That is vs vs a dozen infantry divisions, two PzGr Div, a Pz Div, & assorted Pz brigades.
What it does show is that a thrust towards the Ruhr with a subsidiary thrust towards the Saar does not have to reach the Swiss border.
I'm really skeptical. Note that if the Swiss border is not reached the railway connection between Germany & south central France (Army Grp G) remains available to move supplies or reinforcements in that direction. Conversely the 3rd Army lacks the supplies sent north from Marsailles, which keeps its operational ability cramped to early September supply delivery levels. Vs a 50% stronger defense in raw numbers a thrust towards the Saar looks unproductive.
There is a political question as well. Anyone wish to speculate on how ethusiasticaly the French leaders, or ranks would accept fighting across several mountain ranges to secure northern Italy & hypothetically Vienna? Meanwhile foreign armies are fighting over French territory. I suspect the eight French divisions at hand in Sept 1944 would be of marginal value in any ramped up Italian or Alpine campaign.