No, Oreo is generally better for battery life than Marshmallow.
The thread has a wrong premise. MediaTek does not target the high end, they target mid-range mostly.
Between 10K and 26K, you can find good mediatek phones. Above this range, MTK loses value very quickly.
Performance wise, Qualcomm generally ends up having the better GPU at the higher mid range, for e.g. SD 636/660 vs. Helio P60, GPU wise it's a win for Snapdragon.
But in lower end, Helio P20/P22/P25 is generally more than a match for the SD 625/626/450/630 variants, even GPU wise.
MediaTek phones generally come with better cameras at the lower end (because, developers do not want to put much effort into programming DSP for a low end phone, and MTK has dedicated IP cores for camera and image processing - while Snapdragon has a flexible and highly programmable DSP called Hexagon, complemented by an Image Processor named Spectra). This means that "without much effort" and using the same hardware, the Mediatek phone will generally click better pics.
Mediatek SOCs also have Wolfson/Cirrus Logic IP to handle the audio parts - though not as good as dedicated DAC. Many Snapdragon phones have dedicated high quality DAC and many don't - but Qualcomm's stock one is a bit worse than MTK.
Such reasons give a lot of encouragement to device developers to use Mediatek for low end devices. Qualcomm has tried to fix this with SD 439 and SD 450, but IMHO still lagging. Mediatek was also first to market with Dual 4G VoLTE, which Qualcomm missed (though now there is parity).
For example, at the lower mid range, Helio A22, P23 support Dual 4G VoLTE, but Snapdragon 625/450 do not.
The device makers feel updates and custom ROMs will not be a big deal for lower end phone users, and to some extent they are right. Mediatek is trying to remedy that with a GMS Express program where they will make a regularly updated stock AOSP ROM available for a particular SOC for all the device OEMs....it should at least ensure timely security patches. I am seeing a few vendors become timely on security patch updates with MTK SOCs now.