that topic is alot about information + marketing kf the product. I read that topic till the point where he wrote the 5w means the oil is thin. I think this gentlman seriously lacking to inderstand the viscosity of the oil and its relation with temperature.
Look. If the manufacturer recommends to use 10/40. Then we can use
these oils will work fine.
But if we will use less thinner oils like
etc. The engine will still work. But it will not perform well because we are going against manufacturer's recommendations.
However, if use 5/40 oil, then it will be pretty acceptable. But important is that 5/40 oil is fully synthetic and comes with api sn grade which is again not recommended for bikes.
So make sure that 5/40 should be old grade like sg, sj, sl, then its fine.