I can assure you that milling major pieces out of a block of steel then welding them in place and welding a strap over top is far more time consuming that beating the end of a tube together and seam welding it.
There's a couple reasons for the steel plug method, the first is accuracy. When building the way other manufacturers do you have to cut the tube overly long then fold the top together. This is largely done by eye and the resulting tube can be slightly too long or short and you just make up for that by drilling the hole for your pivot bushing in the correct location. With the billet plugs you simply cut the front and rear tubes of the gear leg to the exact same length every time and drop this plug in which locates the pivots (or gear leg tops) in the same spot every time. Much more precise.
The second reason for it is strength like mentioned. First, down on the axle, the normal method is to just fishmouth the end of the axle and weld a doubler on each side. The steel fork plug at the axle where the shock strut attaches is much thicker and sleeved inside the already doubly thick axle which not only stiffens the axle in the critical junction where the tubes meet it but also creates a much more precise and stronger shock strut attach point. On the gear leg tops the difference in strength comes from fully supporting the bushing along it's entire length as well as not stressing the gear leg tube by cold or hot forming it from its original shape. If you're taking a rolled tube and then forcibly forming it back into itself then welding it that is naturally not as strong as simply welding a plug into the end of a tube that has a straight cut across its end. Like I previously touched on too, the pivot where the gear bolts ride is fully supported along its entire length instead of riding in a thin steel tube bushing that is only welded/supported on each end.
I don't have numbers to support it being stronger (not an engineer, just a sales guy) but I can't see a reason why it wouldn't be after all it is a fair bit more material in all locations than on other landing gear designs that I've seen.