You are pretty much limited to low voltage CPU if want thin notebook...
But its not really that "slow".

Slim gaming laptop, there are, like the Sony S 13'', Gigabyte U2442N. But it cost more than RM2K..

The HP Envy 4 in your link is perfectly capable of doing the usage you describe
You have to understand the "benchmark" and their methodology. The reported figures are average, ULV has wider range of High/Low.

Take i5-3210M vs i5-3317U. Both are Ivy Bridge, 2 core 4 thread same cache.
i5-3210M run at 35W, 2.5 GHz, turbo to 3.1 GHz (turbo by 24%)
i5-3317U run at 17W, 1.7 GHz, turbo to 2.6 GHz (turbo by 53%)
So obviously 3210M have more raw power than 3317U. But 3317U when under heavy load, could perform more or less like 3210M under normal load, so 3317U is no slouch either (of course whether the CPU can sustain turbo mode also depends on the temp, so you need to make sure to keep the laptop cool).

2.5 / 1.7 - 1 = 47%
3.1 / 2.6 - 1 = 19%
(2.5 + 3.1) / (1.7 + 2.6) - 1 = 30%

And slim laptop has less space to dissipate heat, you will why understand brand opt for the 17W ULV.