Even a really slow car would take perhaps 6 seconds to get to 35. What you are describing is traffic congestion. It is not caused by people accelerating too slowly at all. In fact, it's probably exacerbated by people accelerating hard, driving too fast in congested conditions not suitable for that speed, and then being forced to brake. This causes a ripple effect backwards down the queue of traffic.. often miles away from where the actual obstruction is (or was). This is what causes that seemingly inexplicable congestion you describe. Blame it on whatever you want, but if you did your research you'd realise what actually causes it has nothing whatsoever to do with small cars. You need to do some research... that's all.
Why will I need to brake earlier if I'm driving properly? I plan my driving, and use my brain.. I anticipate. I never have to brake hard, and why is that a problem even if I do? As already mentioned, braking harder, and later CAUSES traffic problems, it doesn't cure them

You talk as if you're the only one with a big car.. LOL. At risk of sounding childish, mine's probably bigger.... and I don't drive it as you describe. I also have a very small car.... and there's no need to drive it as you describe either.
You just drive terribly it would seem. If you need "ESP" to safely bring your car to a stop in routine, every day driving.... sorry... you've no business being behind the wheel.
Sounds to me like you place a great deal of importance on that big car.. right up to the point of talking [PLEASE DON'T TRY TO BYPASS THE SWEAR FILTER] in order to justify something you can't really afford. Why skint yourself just to have a big car anyway?
This week's "Talking [PLEASE DON'T TRY TO BYPASS THE SWEAR FILTER] Award" goes to you.... hands down winner.