I also thought about wet bulb and checked the humidity in Delhi, which seems to be just 7 % or so. According to wet bulb calculators that's still good, like around 23 °C wet bulb.
Interestingly the wet bulb temperature calculators that I tried only work until 50 °C, so that was what I put in.
At 50 °C you need about 35 % humidity to get to 35 °C wet bulb.
Regarding your second point: If I'm not mistaken, the hottest month in the region is around May. The temperature is influenced by monsoons, and although the sun peaks higher in summer, it is generally also more cloudy and rain cools of the surface. That's why usually temperatures peak just before rain season.
If Im not mistaken, Delhi's hottest month isn't in peak summer but in May and June, so now. As the climate is largly influenced by the monsoon season.
Next year also doesn't necessarily need to be worse, now going from an el niño into a la niña makes that somewhat unlikely, although regional differences will probably make some places worse, compared to this year.
Please correct me if I'm wrong, but people may be already dying by the thousands. Isn't it rather difficult for a doctor to point down the reason of death to heat?
If not next year, it will get worse rather quick, that's for sure. Much, much worse.