PLEASE IGNORE AND CLOSE THIS ISSUE. As it turns out someone came along and set /gamerule maxCommandChainLength to 1. My bad, and my apologies.

Trying to set up a command block system on friend's realm led me to believe that chain command blocks were broken. I took my system over to a single player world where it worked as expected.

The system was as follows
(I - /gamemode creative Spearkiller) > (C /execute as Spearkiller run tp Spearkiller ~ ~100 ~) > (C /kill Spearkiller) > (C /tell Spearkiller "You don't know how command blocks work") 
where I is an impulse command block, and C is Chain.
All command blocks were set to always active (bar the impulse command block at the start) , and unconditional.

Using comparators I could see what blocks triggered, and what didn't. The result, despite being the EXACT same system:
Realm: https://imgur.com/a/EI2koTK 
Single Player: https://imgur.com/bltp0tw