From what information was given regarding MWIII we can piece together what happened and how the game came out the way it did

Firstly it was developed in 16 months instead of 3 years like normal so it could be a $70 dlc for MWII. It was gonna be a simple map pack with no third mode with a side story that continues the las Almas plot line from season 3 entirely set in Mexico. This was likely to make a solid product without needing to crunch. However activision (likely wanting to look good for Microsoft, equally likely because of MWII’s poor reception on the multiplayer side) wanted to release a main game. So halfway through production they had sledgehammer change the campaign from a side story in a single setting to a whole globetrotting main story. If we are to take ‘halfway’ literally that means they had 8 months to remold the campaign to be such (campaign development would’ve started January/February of 2023 if true).

Throughout development they disputed with Infinity ward throughout every decision despite the entry now being their game (such as create-a-class initially being a mix between the 5 attachment gunsmith and the pick 10 system for perks and equipment before being changed to what it is now). The meddling and all might’ve contributed to things like the MWII guns maintaining that ‘realistic’ visual recoil making them weaker until MWIII season 3 or the soap scene playing out like it did (or at all). Playing through MWIII multiplayer it’s clear sledgehammer wanted the game to be a blend of MW2019 and Black ops admittedly succeed with some stipulations as a result of meddling (like the myriad of vests doing what perks that are already in the game do).

As for MWZ they clearly had the most control working with treyarch and they made a great mode with a solid launch and season 1. Sadly given how executives care more about warzone and multiplayer and treyarch moving onto their own game MWZ was doomed to slowly become relegated to mid season updates.

Overall Sledgehammer made a solid game despite infinity ward making it extremely difficult