The answer really depends.
You heard of people becoming millionaires trading cryptocurrencies, high risk stocks like Gamestop, AMC Entertainment, IPOs , and what have you.
Personally, I prefer a diversified portfolio for a fairly simple reason. It is not easy to spot sector rotation where tech stocks are not falling out of favour and in are the banks, real estate, industrial stocks, etc.
So, that way, when my tech stocks are down, my other portfolio shore me up , leaving my overall portfolio in the green. Please note that all 3 indices are still in the so a healthy correction of 5-10% is acceptable. It is not to be viewed as market as some analysts or the media would want you to believe.
Of course, you may suffer had you bought in recently.
Another thing about this strategy is your domain knowledge of that sector. For example, if you are very familiar in a particular industry , say banks, then you would know how to value it differently from other traders/investors. Still, no one sector is 100% nor all the time but they go through cycles. You need not be an expert at catching at the exact top or bottom but participate at a fairly good price and you still can make good profits.
Think of the sector as a specific sport you like. If you spent a lot of time swimming, then you are going to improve on your strokes, stamina and speed as compared to someone who does it once a fortnight. Same for the sector - you do your research , review the charts more than others, you will spot more patterns, understand the "personality" of the chart and your confidence grow over time as you invest in it.
Others like to have a flavour of different sports as it is more fun that way. Like me, I love running, swimming, walking in the nature, etc. So, you know a bit of each sport but not deep enough to win medals at competition, so to speak.
In conclusion, there is no one fixed strategy for everyone. Find something that you like and you can relate to so doing the research work becomes fun.
so, recently i've slowly rotated from techs to what are considered values (banks, energy, commerce, entertaining), although, when the right moment comes, i'll rotate back to tech, which is my favorite sector to invest in - i strongly believe in the next decades tech sector will be no1, as most companies are involved more or less in tech (from e-cars to robots, biotech, re-energy, AI and so on); semiconductors, especially is my favorite one, due to its multi-industries usage, ecars comes second and cloud-fintech-robots-AI third!