Turns out nobody has done this yet (as far as I'm aware - the only other guides I could find were hacky and outdated), so I decided to make my own Attack/Defend-CTF Hybrid gamemode prefab, with the aim of making it as simple and bare-bones as possible while still functional and presentable enough for a publically-released map.
Contains two playstyles - instant capture (HAARP/Vector style) and timed capture (Dauphin style) - and also a few notes on how each one works.
I'm planning on updating this with multi-stage versions of each playstyle too, but for now, here's a Basic AD/CTF Hybrid™ for your convenience.
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Attack/Defend-CTF Hybrid Prefab 1.2
Simple A/D-CTF hybrid prefab