Not commenting on the quality of advice from GLJ Research, but instead noting that losing money in a bull market isn't necessarily a negative indicator. General consensus of analysts is that the US market is tremendously over-valued. The actual economy is in shambles (at least partly due to the tremendous damage done by COVID), but equities are shooting up and up due to super low interest rates and voluminous input of capital from government entities. In short, the markets show every indication of a huge bubble.
GLJ isn't providing advice to retail-type folk. They are providing advice to institutional investors. These folk aren't playing in your artificially defined timeline of "in the last year." They are looking longer.
So, what do you do if you have a medium to long outlook and the market is in a bubble? You hedge the hell out of your investments. And you short the bubble. The problem is, shorts cost money in the short term. Hedging often is the same. So, over the course of a year, you may lose. Over the course of 3-5 years you may stand to make significant gains while things crumble around you. Michael Burry took some pretty big short-term losses during the housing bubble. I'm sure some Slashdot folk were calling him out as an idiot because he lost X amount over a one year time-line.
Is this particular guy right? I don't know. Does it make sense to call him out in a bull market for picking positions that lost around 10% in the last 12 months? Definitely not. If he's hedged/shorted well his position could see a meteoric rise while the rest of us watch our 401Ks lose 60%. Not saying this will happen, but it doesn't seem outside the realm of possibility - at all.
This is not financial advice, but an obersvation. I have no position in Tesla. I would like to see electric vehicles (and Tesla) continue to succeed in the marketplace.