Squiddlioni

Twitch (and YouTube currently) switches to a new content stream to play an ad, which is easy to detect and block in an extension. If I understand the tech correctly, server side ads would be stitched into the playing content stream. The extension would have to know the content of the video to know that an ad is playing. There are some clever ways that might be caught (looking for spikes in bitrate, volume differences, etc), but none of that currently exists in the software in the OP.

The small one’s Stun, big one’s Kill

It’s called Brook’s Law. It takes a lot of time and effort getting people up to speed, and that takes experienced devs away from coding. You also have to get them credentialed, teach them the tools, need extra code reviews/testing/bugfixes while they learn the quirks and pitfalls of the code base, etc. In the long term you’ll be able to get more done, but it comes at the cost of short term agility.