Brother,
Very less oil changers gave the original advice.
Mostly gave the advise to use oil abc because of their profit margin in that particular oil is more.
So its less about the engine's actual requirement and more about the money.
If you've Altis & Reborn, both are under 20K and you are using 5/30. Its really good oil. Don't change it if you are not comfortable with 5/40. But at-least choose this 5/30 oil from the good companies like
. PTT Performa
. Volvoline
. Liqui Moly
. Mobil1
If you still don't trust on these companies, then at-least feed your cars with
ZIC XQ
Or
ZIC OW
These oils are far & far better than Shell, Total, PSO, Toyota, Suzuki, Caltex, Kixx, Sinopec, SIL, etc.
Cheers.