RE: <font color="red"> Why does the GL3430 weigh 705lbs more than the
L3400? </font> The 3430 is designed to be a bear in the woods that will knock things down, pull things out, and rip stuff up. The
L3400 is one of their economy designs, it is a good mix of power, size and weight for people who may not need the 3430.
RE: <font color="red"> does weight = pulling power </font> In simplistic terms the answer is YES. In practical terms things get a bit muddy. But if you want a tractor to pull things, get a heavy tractor. For your purposes as you outlined, I'd suggest a heavier tractor than a lighter tractor. Understand that for many users, weight offers no advantage, can actually be a liability, and for some users it is an asset. A typical 5, 10 or 15 acre homeowner, who uses the tractor for almost everything, needs a "Swiss Army Knife" in their tractor choice. Kubota B series tractors are like that. They do everything, some things well, some things adequately. But you want it done and a B series will do it. Their light weight will mow without rutting. Their small size will fit between trees and shrubs. Their loaders a capable but not best in class. Their mower deck cut quality is nearly legendary. They offer enough wieght to give adequate traction to pull proper size ground engaging implements, but they won't win any plow pulling contests.
<font color="red"> What's the idea with making such light tractors? Is it really basically for mowing purposes? </font> To really deal with those, take a look at a lot of USEABILITY factors and take a look at the POTENTIAL CUSTOMER BASE and that customer base's INTENDED USES. So who buys light weight Kubotas? They are very popular with landscapers and homeowners. Landscapers like light tractors because they are easy to pull on a trailer, because they don't damage the grass in a yard they are remodeling, because they don't do a lot of pure ground engaging type of pulling. For the most part, small property owners have similar types of uses. In particular, a "B" series Kubota is designed ot be a light tractor series, they have lots of PTO HP for its weight to power implements, they still have sufficient weight when used with proper sized ground engaging implements. These are great mowing tractors, possibly the best. They easily handle rotary cutters, tillers, PHD, snow blowers, etc. Weight is not much of a factor with those implements but PTO power is. They are pretty good with a box blade, but a heavier tractor would be better with a box blade.
The grand L series are designed to be heavier and they are for differnt types of jobs. Most people don't mow around their tulips and across manicured lawns with a heavy tractor.