Asking a Veteran Player, they confirmed the Wall Segment Limit.
This Limit is: 260
They also confirmed the Defence Platform Limit:
This Limit: 18
Heavy Platforms are also limited to: 4 (though AI NPC Bases don't abide by this Rule, Logic Failure)
Now, considering what the Maximum Stats of these are, at Maximum Level...
Wall HP: 880,000
Defence Platform HP: 2,700,000
Heavy Platform HP: 5,400,000
Considering the Average Damage Rating of a New Unit:
Burst Damage: 3,500,000 DPS (generally over 9,000,000 per Shot)
Sustain Damage: 7,000,000 DPS
Area Damage: 6,000,000 DPS
OK, I think the point is made with that.
In the event it's not...
A Player has to choose to Defence a Single Structure in the Middle of his/her Base, and has a limited number of Defences and Walls to do this with.
I know this isn't Supreme Commander or Command and Conquer, but nobody uses that limited number of defences to protect their base. On average, Command and Conquer at Tournament Level: About 50 Defence Structures can be placed by the Average Player, and 200+ by a Turtle Player in a single match. In no case are they One-Shot-Kill from any single Unit. Watch Tower (CNC3TW) VS Mammoth Tank, it's still two Shots. OK, those two shots are fired quite quickly, but it's still two shots. That is the Weakest Defence against the Strongest Unit in the entire Game.
Comment: Broken Game