What Nextgrid is saying is a common, incorrect stereotype.
"Is it really profitable to get in, like now?" Yes, but... Long version: Yes, you will make your money back within 2 years almost guaranteed on a new mining rig. There is a minimum cost to get in. For example, at a minimum, you will need a good card at 3k+, which puts you at 3.5-4k just for price of entry. However, you will make that back within a year.
Now the heavy BUT:
1. No one knows what will happen once ETH switches from mining to proof of stake in 2022. Mining profits may go to 0.
2. If BTC price goes to hell, so do your profits in the long run. This is price-risk, regulatory-risk, etc.
3. There are heavy tax implications and a lot of management. For example, you won't get the returns mentioned if you don't properly account for equipment costs.
4. Once you want to make more than $10 a day, there are heavy, heavy set up costs - cooling, proper power supply, etc.
Finally, profitability of mining is back because China is actively banning crypto mining, so other areas can compete now.
"I don't think it was ever profitable unless your energy prices can compete with what industrial-scale miners get in favourable locations (right next to a power plant in an area with too much surplus power, etc"
This is simply not true Nextgrid, see https://whattomine.com/ for roughly-valid numbers. Note that BTC is not anywhere on the GPU list - you do need extremely expensive ASICs to mine BTC. You also need to order them from China, pay a 25% import tax, and overall risk quite a bit.
Final note - if you could get GPUs at cost or MSRP, you would be in pure profit in less than a year. The problem is that a $2000 GPU is marked up to about $3500 atm.