Twice as long, not a few more minutes.
Imagine I want to make, for example, a house. If my interior is 16x8 (and it will certainly be much larger than that), it will require two stacks of wood (planks) to make. That means that, pre-nerf, I would need 32 wood logs (which is a lot for me, because I loathe chopping down trees). Post-nerf, that's a stack of wood logs.
That means that the floor alone of my tiny little house (16x8 is TINY) will require a whole stack of wood.
Now, at the time that I'm making a basic starter house (the only reason that I would make such a small house is to protect myself from creepers and stuff whilst getting set up) I'm only at basic stone tools, so blocks break slowly.
OH WAIT, greg nerfed stone tools too... hurrah.
Basically, to get ONLY MY FLOOR going takes a whole stack of wood chopped with an axe that is horrendously poor quality because greg nerfed it, and I couldn't use iron anyway because he nerfed that too. That means that me getting into the game, even going caving, is delayed by a VERY long time and it screws with my playstyle. Sure, some people like to leave their stuff out in the open, but the problem is that every single thing in the game requires wood at some point. And as you said, this in no way adds difficulty. Unless you're doing it at night, there is absolutely no danger to chopping trees, just tedium. Some people find REGULAR tree chopping so tedious that they have to install a treecapitator mod...