I've said SEO, optimization in so many other threads. If people would look at the sticky's as I, and others often suggest then they would know that. But it takes more than good SEO and shoutouts. It does take persistence. There is a saying half of success is showing up. Many people quit if they don't have 5000 subs in two weeks. You're right about the three things listed but I would round that list out to 10 important things, and persistence would be included. Btw, I have to disagree. This forum isn't perfect but terrible? Come on Flammy.
Persistence
Choosing the right content
SEO and/or Shoutouts
Thumbnails
Promoting
Regular Uploads
Uploading many videos (unless you are doing something incredible specialized/ or have established a large audience)
Quality content (most of the time, everything can't be a masterpiece)
Collaborations
Connecting with viewers/subs
I would also like to add that different genres require different strategies for success. Some things work great for gaming channels that don't work the same way for vlogging channels.
I'm going to be posting my own thoughts on 'secret to success' soon, so I've thought about this a lot lately. On the persistence factor, I really must disagree. This is how I made my short list... first think about everything that helps (and persistence does indeed help) and rate everything with one of the following: high/mid/low importance in terms of 1) how important it is to success 2) how difficult it is to do. For example social media is one of the few things I give a 'high' rating to as it is very easy to set up and can drive a lot of of traffic. The list was made up of concrete actions or aspects, but if persistence was on the list I would give it a "mid importance" or "low" rating of importance.
First of all it obviously isn't critical to success. I think everyone here has seen channels which clearly don't try yet the views and subs fall into their laps. Not all cases are that extreme. In other cases where people quickly find success the success itself is the motivation. Either way, I think it can be important to some people (especially channels which don't find success right away).
Secondly its a fairly common belief that persistence will eventually lead to success. Perhaps, but if you find success thru persistence like that it is dumb luck. I think people should work towards success rather than merely keep making videos destined for obscurity hoping one of them hits it big. YouTube doesn't credit effort when it rates or recommends videos... just success/results.
As for the other factors:
Promoting - I would consider this the same as SEO and shoutouts. Sure, not exactly the same, but all under the umbrella of 'driving traffic'
Regular Uploads - If this refers to say uploading on a schedule you try to stick to (1 per day, 2 per week, 1 per week, 1 per two weeks, etc) I do not consider this important what so ever. Production speed obviously depends on your quality/style, but I don't consider channels who upload 5 videos in one week then nothing next week to have a huge issue. TL;DR: Helps, but is not required at all.
Uploading many videos (unless you are doing something incredible specialized/ or have established a large audience) - Same thoughts as regular uploads. TL;DR: Helps, but is not required at all.
Quality content (most of the time, everything can't be a masterpiece) - I think this opinion will surprise most people... but quality doesn't matter. Yeah, seriously. I have had the somewhat rare opportunity to be able to follow my niche has it has grown from about 3 channels uploading on a semi regular basis to a well established niche of 10 large channels (~5k subs+) plus hundreds of smaller channels... and the people who grew the fastest by no means had the best quality or even good quality... they merely got the content and the right time (a subset of getting the right content). In terms of literal video quality, same story. It depends on your content, but by no means is 720p+ required. To this day I still upload roughly 70% of my content in 480p (rest is 720p). TL;DR: Helps, but is not required at all.
Collaborations - I would consider this the same as SEO and shoutouts. Sure, not exactly the same, but all under the umbrella of 'driving traffic'
Connecting with viewers/subs - I would consider this low importance. It doesn't scale well and is isn't unimportant if you DON'T do it... so once again... TL;DR: Helps, but is not required at all.
In terms of vlogging vs gaming - I think vloggers have it much harder. SEO is harder as well that it seems to me, an outside observer, they are all bundled to gether with it hard to differentiate between the channels... aka gamers are split between platform (pc/xbox/ps/social/mobile/etc) as well as by type of game (shooter/strategy/action/rpg/etc) as well as by game itself (CoD/BF/TF/etc). All that said, I think it is equally valid that it comes down to 1) Content and 2) driving traffic (still, primarily thru SEO or shoutouts, but those others can work too (colab, promoting, etc)
In terms of this forum being terrible - I stand by my words. They aren't nice words. But this thread had 30-something replies before I considered anyone got close to a "good" recommendation. A few people had tried. I counted 4 comments were the advise actually answered the question rather than joking around. 10% helpful comments, roughly 10% kinda helpful but not answering the question, and 80% joke/unhelpful responses...? Well perhaps we have a different definition of terrible.