"Sensible" is an odd word when it comes to investing. What is sensible for one person would be reckless for another, and overly cautious for a third. People have different comfort levels with risk, different timelines when they might want to use their money, and different goals for their lives.
If you might want to retire soon and start spending your money to support yourself, then "investing for the long term" is not sensible. You need stability, not an extra 5% that comes with a risk of a bubble popping. On the other hand, if you have enough money to live on outside of these investments, and are just trying to make higher numbers appear on statements but it would not harm you in the slightest if those numbers crash for 5 or even 10 years... then sure, it probably is sensible.
Most people fall somewhere in the middle, and want diversified investments so that if one piece crashes, the others hold up, and you get a return that is in the middle, with a risk level in the middle.
