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As a footslogger in the 60's, I am sure myself and other combat vets on here can assure you that the 'wait in ambush' is an integral and important factor in ground combat. Both for Infantry and Armored units. The trick is to either extract and call in support (or the tards as we affectionately call them), over the horizon Arty which we don't have, or get the heck outta there until you can amass enough force to overwhelm the ambush. So the simple answer probably is 'Yes', spawn ambush is a valid strategy.
I served in an armoured regiment in both the regular army and the reserves from 1993 until 3 weeks ago.
I agree that in the real world, ambush is a vital part of armoured operations, as is the use of artillery and air assets in neutralizing enemy forces, that's all well and good.
In game I honestly believe that the nature of spawn camping tactics destroy the essence of the fight, in as much as it removes almost 100% of the skill level involved for the camper, not withstanding the skill required to find a good hull down ambush point.
When this is multiplied by a factor of 4 or 5 campers, the opportunity for the spawning vehicle to fight it's way out is almost completely negated.
Lusches chart shows a randomised spawn pattern, I didn't know this happened but on closer inspection, the spawning occurs over a 2500 ft or 850 yard radius, of the 20 spawn points, no less than 9 fall within the centre 1/3 of that radius, for the guy camping the spawn point this equates to a tank appearing over an area of 300 yards from the previous spawn point half of the time. Hardly a stretch for the entrenched player to be able to locate and hit, especially if there are multiple enemy cons camping.