Direct battlefield experience from WW1 contradicts you both.
Couple of reasons for this.
- Suspension was either very crude or non-existent on early vehicles making aiming very difficult unless stationary. Machinegun's got around this by volume of fire and were still effective.
- The early HE available for shell filling was less powerful than the stuff available in WW2 for instance. A 6 pound HE shell in WW2 would be more effective than the WW1 variant. This meant that you had to be bang on with you accuracy to be effective. A situation made worse by point 1
This all added up to the first large scale order for tanks with the Mk IV being predominantly female (all machinegun) versions. This only changed as Germany began to deploy both captured British and their own tanks (A7V). Then the Hermaphrodite version was created with a split of cannon and MG armament.
This is the right idea. Properly used artillery was more effective than tanks in the 100 days. If an offensive had tanks but no artillery it was more likely to fail than an attack with artillery but no tanks. Of course true combined arms was the most effective.
As it stands right now though ITTL we are a long way off of any 100 day type action. The British and French could not pull that sort of tactical maturity off but they don't need to. This isn't a 1918 German defence they are facing it is a thrown together 1914 German defence and that is a lot weaker. Anything well prepared enough to stop an armoured car with MG's will be able to stop an improvised armoured truck etc with a small cannon. Artillery will be needed for places like that and then you are back to being armoured cars with MG's are enough to tip the scales.