Cross-checking my dad's advice: is this a case of timing the market?

I am a new professional, never invested and have ~$40k. Long story short, I got hooked onto finance and FIRE stuff and ended up on jlcollins blog (jlcollinsnh.com).

I like his idea of simple investing into VTSAX, and letting it growing over time. I told my dad I would invest in VTSAX/index funds soon.

Wanted to cross-check his advice: - with the current market high, I should invest max 60-70% of portfolio into stocks (keep the rest in bonds, etc.) as he is pretty sure there is upcoming crash soon (I asked for specifics and he said within 5 years) - and generally as the market rises, your stock allocation should decrease regardless of your age (although you can be more free with it if you are right off the heels of a crash like 2009). But right now, with a 2009-level event so long ago, I should be careful. So for example, if the market rises 30% next year, I would want to bring the 60% down to 40%.

Is this not timing the market? I thought it was a fool's errand to time the market. My understanding is if you are at the start of your investing life, history shows that long-term it all averages out to be the pretty much the same regardless of when you start investing.

He did mention that while you don't need to pursue exactly timing the market, you can roughly time the market and lead to better long term gains (so for example, it being so long since a 2009-level crash warrants restraint).

Isn't this exactly what causes those who time the market to lose out long term because why they may avoid really bad crashes, you also avoid really good gains?