Do you want the truth or the convenient lie? Convenient lie is that Deli worked for all those subscribers. The truth is that she had help from EA. Big companies have lots of paid avenues that regular channels do not. Why does every movie/tv show/triple A video game trailer end up on trending with basically no views and gets pushed to everyone through recommended? Because the company pays Youtube to promote it. Susan Wojcicki (YT CEO) has admitted to forcing videos on people that she thought were important and she was filmed talking to a rapper, saying things like "Youtube would do whatever they could to help him get his views up." Trickery and fakery happen all the time. It would not surprise me in the least if EA paid to promote their shills content instead of actually putting out their own. I'm sure that is cheaper overall.
Just some food for thought. When Deli uploaded her video about the Generations pack coming, her video was at the top of searches for The Sims 4, beating out Lilsimsie who had more views and faster view velocity. I wouldn't say Deli's video took off like a rocket, being a full day after everyone else uploaded and it didn't get that many views the first day, so why was it at the top?
If you want to learn more about the shady crap that goes on with paid shills and reviewers, I recommend this video. I cued it up to the pertinent time stamp and the conversation is about 5 minutes long. Definitely worth a listen if you are interested.