Is investing in stocks already heavily favored by ETFs smart? Furthermore, is 100% stock portfolios worth the risk?

I left a comment elsewhere which after posting it made me curious about making it a post. Forgive me if I spell something incorrectly, English is not my first language.

https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4590406

So I read this paper about 100% Stock portfolios after watching a YouTube video on it (multiple out there).

And I wondered how I’d go about choosing the stocks I’d invest in. I did so because just last year I didn’t touch stocks but when I went on my app on my iPhone (Stocks) and saw how much I could have made had I just invested in stocks that were already a big presence in almost all of my ETFs the. I’d have more value to my name.

To look at it I viewed an era that had large fluctuations in which I invested in which lead me to 2019 to 2024 because in-between that we had the fed-induced boom and the crash that came before that along with other crazy fluctuations.

So for my example I used march 2019 to March 2024 (which had steep decreases and increases):

1.MSFT: 250.92%
2.Apple: 248%
3.Meta: 176.44%
4.Googl: 149%
5.Amazon: 96.46%

1.QQQ: 140.45%
2.VTI: 84.34%
3.VOO: 81.39%
4.VT: 54.38%

Here is the Summary of percentages those sticks hold for each ETF:

1. QQQ: ~41.3%
2. VOO: ~22.2%
3. VTI: ~13.0%
4. VT: ~6.1%

It’s not like investing in Meta, Apple, Google, and Amazon is unheard of, they already make a huge part of all ETFs you come across that measure commonly used domestic indexes. So… is this the way? I truly want your critique on this because if it works it works and if not then it doesn’t, it’s not about proving I’m right it’s about maximizing my understanding of investing.