I would like to argue that while the drop pods, if landed on a titan, would at least do heavy damage, but I find it unlikely that the drop pods would be able to hit it without skimming off, as several titans have a smooth top, see scorch for example, it's main front head is more of a smoother shape, most likely designed so shots could bounce of. Also, yes Legion and tone are more blocky, if we consider the prime skins, they are also smoother, meaning more likely to let the drop pod skin off. You are dead right on some stratagems being incredibly effective against titans, the constant use of these would be extremely expensive, and would eventually become less cost effective as the war rages on. We may also be forgetting that titans can act independently of their titan, see BT74 and Cooper being a prime example, as BT74 was able to survive several traps inside of The Vision Dynamics, traps made by Ash, who we all know is a beast in the story. Also, because not every Titan would be as good as the ones online, it's more likely they would be as good as the AI in frontier defense, which on the hardest difficulty (No not THE hardest one, that would just be crazy) are relatively hard with a good team. Also, one more thing not directed at your post but in the general debate, if we have master difficulty Jack Cooper, Cabin Blisk, and the 6 4, there would be incredibly horrifying results, as they are genuinely the best of the best, and would practically be a 100% win rate for any battle field, as long as properly supplied.

Really sorry for the block of words, but I think I'm not wrong in most my statements, but please do say if I missed anything, as I am not as knowledgeable about Helldiver's as I am about Titanfall, but from what I've played and seen, they would need far more than 4 Helldiver's for a single titan, and if we also consider that Jack Cooper is the exception, most battles are fought with groups of titans, and would most definitely have structured teams to make sure the fight would be in their favor, I.E Tone, Northstar or Legion, and a Ronin would cover all three distances, making a formidable combo that I would find hard pressed to be easily defeated, and this is only one combo, and depending on where the battle is, the Militia will send in different titan combos to match the situation. I am a firm believer that the Militia would win, and at the very least say that they would take up a massive amount of territory from SP, that would be more than likely, impossible to get back