Why is it the old Lancers are inaccurate and slow firing while the new one is accurate, faster firing, and chews through ammo quicker? It's hard to see how one grew into the other until realizing the retro lancer was an offensive weapon, used for constantly redeploying closer to the enemy and charging forward. Whereas with the modern Lancer they've fallen back to Jacinto and needed something that could function while holding a single location.
The Locust Horde is by no means primitive technologically, instead using Organic Technology as counterparts for COG developments. The COG use more familiar machinery, instead running on the gasoline-like Imulsion. However, this discrepancy in technological development makes sense lore-wise as well. Humans harness Imulsion, which is actually what's killing the planet, without knowing the truth behind it. The Locust, developing underground and living next to the stuff, would have discovered its danger long ago, prompting their development of biotechnology (which would never need Imulsion).
Why is it that the locust drones are smaller and weaker than the females of their species, the Berserkers? In reptiles, the females are always bigger than the males, and Locust are a species of underground-dwelling lizard men.
In Gears of War 4, the Deadeye DeeBees are pretty lousy shots, even on Insane difficulty, compared to what human players can do using sniper rifles. They often miss badly and very rarely land headshots. Since the Shepherds never had much of a job in combat other than to suppress/detain possibly unarmed civilians, they wouldn't need to be totally accurate in order to be effective. If some average Joe is causing trouble, they could simply fire a bullet or two in his general vicinity, and he'll probably just take off.
In Horde 3.0 (featured in Gears of War 4), the player can use decoys that look like humans and can be used to distract the enemy, fooling them into thinking the decoys are actual living humans. Decoys draw the attention of the Swarm far better than they draw the attention of the mechanical DeeBees. It makes sense, because robots don't rely on sight as much as an organic creature; they can detect vital signs (heartbeat, breathing, body heat, etc.) that an inanimate object wouldn't have.
The reveal of the the Locust/Swarm Hive Mind in 5 makes the scenes where Queen Myrrah narrates and issues orders to the Locust in the previous games more than just dramatic license; we're actually hearing what the Locust heard during events like Kim's death and the ends of Gears 1 and 2 where Myrrah is musing about humanity and the Locust.
The title of "Gears of War" starts to make sense when you recognize the recurring theme in the series (the inevitability of war due to human nature). The main governing body (and one of the most prominent members of the various war efforts) is called the "COG" while its soldiers are referred to as "Gears." What are cogs and gears but small pieces which come together to operate a larger machine? The COG and the gears are components that make up war, as are the locusts and the various factions who oppose the COG, each doing their part (if unknowingly) to perpetuate a cycle of violence and cruelty. "Gears of War" doesn't refer specifically to Marcus and his team, but rather envisions war as being like a machine of which everyone is a piece- a cog or gear if you will.
By Gears of War 4, humanity, or more specifically Baird, has created the android race of DeeBees to assist the remaining human population in labor and protection from outside forces. However, if you play through Horde, you'll notice that the DeeBees aren't very interested in attacking the Swarm. Why exactly is that? Well, if you played the campaign, you'll see how the DeeBees you fight are colored blue and they're only really attacking you because you are breaching unauthorized areas and JD and Del are traitors to the organization they serve. Towards the end of the campaign, a Pouncer shoots one of Jinn's avatars, causing it to turn red and nearly strangle JD to death. Now, what color were the robots in Horde again? That's why the DeeBees don't attack the Swarm: they hacked them. They took humanity's biggest allies and turned them into mindless killing machines that can cause just as much destruction to humanity as the Swarm can. Imagine if they were able to capture huge warehouses full of offline DeeBees and sic them on humanity with them being none the wiser. Imagine standing behind your robot army, fully expecting them to annihilate the creatures threatening your species, but for some reason, they turn their guns on YOU and speak about how "you will be dealt with harshly." The Swarm could easily add another faction to their army, turning a war between man and beast into a Curb-Stomp Battle in their favor...
This has officially become Ascended Fridge Horror, as the Gears 5 trailer shows exactly this happening. While the Swarm is not deliberately trying to do it the DeeBees are being infected by fleshy tendrils from the Meat Moss they spread, turning them against their human creators.
More gameplay from 5 shows that a particular breed of Swarm that resemble a school of airborne eels/lamprey from hell can swim through the robots and leave some of them behind to control it, meaning that the corruption is partly intentional and Jinn's tin can army is a huge liability instead of humanity's defenders. Baird's protests about the weaponizing of his creations become much more disturbing since he was probably more worried about a police state enforced by Mecha-Mooks than handing humanity's sworn enemies a seriously effective weapon.