The general idea is to carry the log and it needs to be that long to carry a 16 foot log completely off the ground. I need the center point of the log closer to the tractor than the point held by the hoist in order to keep weight on the three point hitch. Otherwise the weight of the log would want to raise the three point hitch and that creates a problem. If the log is too long and I have to drag the back of it on the ground, then yes it can be difficult to drag through the woods, but you would be surprised how easy it is to pull it and make a ninety degree turn in the woods. I pulled out a few 27 ft logs over the last few weeks and didn't have a problem at all.
I have not attempted to pull a log on highly uneven terrain yet and probably never will, so I'm not concerned about that. Again, the only reason to have an arch this long or longer is so you can carry it completely off the ground. If I was to have a new arch built, I would actually make it a bit taller and a bit longer in order to carry larger and longer logs, but this one works great for my needs, so I doubt I'll spend the money for a bigger one. If you aren't interested in carrying it off the ground and only want to drag the log, then this setup isn't what you would want. I've seen several much shorter arches used specifically for that purpose. They would be cheaper to build as well.