Let’s assume for a second the European alliance system didn’t work as planned and only Germany and France go to war in 1914 how will this turn out militarily?
For me, this is an interesting potential conflict. I'd start off with the French DoW against Germany being something along the lines of the 1870 war, where the French are somehow seen as the initiators of the war, and thus her potential allies refuse to jump on the French bandwagon, and they end up in a one on one war.
Germany cannot go all in on breaking France, annexing parts of mainland France, grabbing up her entire colonial empire, and going all reverse ToV levels of stupid.
Will Germany be able to withstand French attacks across their mutual boarder?
For sure.
Will France try a naval attack on Germany or vice Versa?
Naval war against Germany proper, nope. Naval war against the German colonial empire, for sure. A poor man's blockade, merchant shipping/raiding and the like, also a given (and potentially the most entertaining/interesting part of this hypothetical war).
Assuming Belgium Is not involved, do Germans have the ability to attack France?
Yes. I foresee many causalities, with little to no advances back and forth, followed by a stalemate/trench warfare. Just how bad this will be for France will depend on how quickly they realize that they cannot push the Germans out of AL, and have to shift the war's focus to something other than frontal assault of an increasingly well fortified boarder. I have no thoughts on how long this will take, nor how many must die of either side before this happens.
How does the French artillery compare to German?
Not really an area of expertise for me, so I'll leave this one alone.
please ignore the political aspect in this scenario
So far as possible, I would speculate that the Germans have to be wary of actions that draw in other nations to the conflict, so the least amount France occupied by Germany (especially in the channel), the better, at least until diplomatic efforts have failed to get either the US/UK in intervene diplomatically and bring the French to the negotiating table. Germanys actions must not seem like this war is about conquering metropolitan France, but some modest gains in overseas territory (Outside of the Caribbean) should be expected to occur.
For me, this war would best be played out over a number of years, with the Germans taking only limited portions of French territory, and then going over to the defensive (in Europe), and awaiting France to come to her senses, and make peace.
1) Fight quickly to take what you can, before the French have fortified to the hilt, and then just turtle up, and tell the world that you are willing to end the war, if only France can be brought to the negotiating table. France can gain nothing, and must renounce ALL claims to AL forever.
2) Make sure everyone knows that Germany is willing to make peace, as above, if peace is had soon. The longer the French continue a hopeless war, the more that she needs to loose at the peace table.
3) I would be very interested to hear how the commerce raiding/blockade aspects of this war plays out.
4) If the ground war can go on, with the pre-war boarders being on the front lines, or behind German lines, then Germany is out nothing, and the burden of the start and continuing war is clearly on France, then international opinion will more and more shift in Germanys favor.
5) Germany would in my opinion, be best served by taking limited areas of European France, and then fighting on the seas.
6) The German Navy has some design choices that limit what they can achieve against France (outside of a stand up engagement between fleets), so the war needs to see the Germans building a new, globally deployable force, so that they can carry the fight to Frances Empire. I would see this as mainly a cruiser war, but these new ships need to have long range/long duration voyages as a central aspect of their design, unlike the OTL ships.
7) Both France and Germany will be stronger than their OTL analogs, as neither will have lost significant portions of their trade/territory, but this altered balance will initially help Germany more, and later on come to favor Germany more and more.
1914: Initially take as much of France as you can, then hunker down and start talking peace, while standing on French soil, and fighting them tooth and nail on the worlds oceans, and start building long range ships, that have proper crew accommodations for long duration voyages as the central design change, as well as the logistical train to support global operations. If there is no prospect to getting the French navy into a decisive battle anytime soon, look into long range BC asap.
1915: If France proves to be stubborn, make limited advances/offensives, keep attacking their shipping, keep building new, long range Naval units.
1916: As above, keep telling the world that you are will to talk, and put the burden on France to come to the peace table. Continue your long range naval buildup.
1917: Some time around mid year, you will see Germany start commissioning her new, fast and long range BC, with more being ready month by month.
1918: Once Germany has the fleet train, and a large number of fast, long range BC in commission, begin taking the war to the French colonies. Make sure that you keep telling the world, that as soon as France makes peace, the fighting can stop, but the more colonies that Germany is forced to take, the more that will not be returned postwar.
Anyway, those are my thoughts for the setup you have outlined.