The counter argument here is "we don't need new people" but I find that to be short sighted.
No Adam the counterargument is that there are different video series aimed at newer and older viewers, or there should be.
When I started watching AH in early 2013, my hook was Rage Quit, which is made to grab new viewers - each video is short, the humor is self-contained to one video, and it's funny within the first 30 seconds. The next series I gradually started watching was Minecraft (which was still only a 30-minute format around the time I started watching AH).
Compare that to something like The Patch. It's an hour of slow-paced discussion with few jokes. You can't jazz that up with a clickbait title or thumbnail. It's inherently not a good video type to grab new viewers and subscribers.
If AH/RT is having problems growing the audience the solution is to balance out their longer-form work with short, catchy videos.
Look at your own success Adam. Why is that that so many long-time AH viewers who knew nothing about IG had no problem hopping on board with your shows? Because you edit your videos to be short, instantly funny, self-contained, in short, "grabby" to the viewer.
AH/RT's problem, imo, is that they haven't exercised control over their video formats. In particular:
Let's Plays have gotten longer and longer, Minecraft is now consistently an hour - it's not the number that's scaring new people away!
Series that were originally conceived as short, grabby vehicles (like GO, HUNT, and VS) are now either boring or overlong.
Rage Quit moved to biweekly and Play Pals (originally a similar length) is now also trending to 15-20 minute format.
Shorts are now rare, Quickbits was discontinued, etc.
Thumbnails and video titles are just a band-aid on the fact that AH/RT doesn't produce enough genuinely funny 5-minute long videos.