Tanks weren't huge in WWI, at least not until 1918. The technology was too rudimentary for them to be really effective. Tanks were first used in combat at the Battle of the Somme, and specifically beginning in September 1916, which is a full two years before the war ended. And they were used in large numbers by the British and the French throughout the war thereafter.

Tanks conferred an advantage, certainly, but only a conditional one. WWI tanks were slow, poorly armed and poorly armored. They broke down constantly, and the Germans quickly developed something of a disdain for their clumsy blundering, and just as quickly designed weapons and tactics to destroy them, from re-purposing field artillery for direct fire, to basic steel-cored rifle bullets that, if fired at a high rate from a normal heavy machine gun (of which all the combatants had thousands upon thousands) could destroy a tank. These also included early anti-tank rifles, which just used a huge rifle bullet, close-in explosives like bunched grenades and plastic explosives, and anti-tank ditches.

The exception to the above was the Renault FT-17, a light tank that was built by the French in 1918. It was a fairly modern tank design, greatly resembling interwar vehicles, with its relatively high-profile central chassis and carriage, its enclosed treads, and, above all, its turret. The FT-17 was the only widely produced tank of the war with a full 360-degree turret, which confers a major advantage, over the clumsy sponson-mounted guns of the British Mark I through V tanks, or the equally clumsy fixed-forward guns on other French and the one German tank (the A7V, of which the Germans built only 20 in 1918). Of course, turrets came at a cost of increased weight and increased manufacturing complexity. In any event, the FT-17 would go on to serve with distinction, worldwide, until 1949.

The Germans, as you may know, had few tanks in WWI, and ironically, it is perhaps they who could have benefited the most from them. The Germans waged war on a paradigm known as Auftragstaktik, or mission-type tactics, which placed great emphasis on individual initiative of junior officers and non-commissioned officers in exploiting developments as they occurred on the battlefield in real time, and concentrating as much force as possible into a single point of maximum effort.

The apotheosis of this paradigm, in World War I, came during the Kaiserschlacht (or Spring Offensive) beginning in March 1918, when the German western forces, reinforced by a horde of veterans brought newly from the conquered east, intended to sweep away the British and French before the Americans could arrive and organize. By this time, the Germans were well-equipped and trained to use infiltration or Hutier tactics, which were a kind of high-energy small-unit infantry tactics, which called for small, but incredibly heavily armed units (light machine guns, submachine guns, flamethrowers, thousands upon thousands of grenades) of veteran soldiers to assault key positions in the enemy line with surprise. These tactics had been very effective against the Russians and the Italians, and now would be put to the test in the West.

And initially, success was enormous. Huge advances were gained, but problems immediately emerged. Due to the junior officers' willingness to exploit opportunities, the advances had gone in many unproductive directions (the main objective, if there was one, was the railhead of Amiens, which sat at the junction of the French and British lines; the lack of a clear objective was another main problem with this offensive and one of the symptoms of too much reliance on mission-type tactics). So the Germans had captured a ton of territory, and made a lot of geographical progress toward Paris, but had not captured much of strategic value. And due to the extreme competence of these units, they were far, far ahead of their reinforcements, and they were then required to hunker down and wait, trying to hold trenches from being retaken from the wrong direction (i.e., the captured trenches faced east, not west). As a result, the infiltration units, the cream of the crop, came under heavy Allied counterattacks, including from tanks, and took horrendous losses. Within about two months, just about all of the veterans were casualties and the reliance on mission-type tactics had led to yet further useless advances.

Amiens was finally reached in August 1918, but by then the German army was virtually denuded of its experienced soldiers and most of its equipment, and the Allies easily defeated the Germans at that city. What followed was the 100 Days Offensive, which broke the back of the German army, and included a return to mobile warfare, aided by, you guessed it, the Renault FT-17.

And now I return to my original thesis. One of the main problems the Germans had in the Spring Offensive was that their infiltration units couldn't really go any faster than a man could run, and they couldn't fire anything a man couldn't carry. As a result, they lacked the mobility and the firepower to turn their exploitations into routs of the enemy. In reality, many routs start with a breakthrough in an unimportant place, but which allow the forces breaking through to run amok in the enemy's rear and destroy their communications, supply lines, and their command. This kind of thing is older than Alexander (they used horse cavalry back then for this, which was not viable in any sense on a WWI battlefield).

So, the Germans in the Spring Offensive had enough resources to break through the line, but not enough to really get into the enemy's rear, because the enemy that was retreating from them was just as fast (or faster, since they actually had tanks), and about as heavily armed (maybe more, again, tanks; and the Allied infantry weren't as festooned with weapons as the German infiltration units, they were no slouches either). That was a major problem, and made it impossible to really hit the enemy's critical rear-echelon functions where they needed to be hit. Tanks, the A7V included (it was a pretty good design for an unturreted one) would have provided the firepower and mobility needed. As they did in WWII, in which the technology caught up with the tactics.