There is no such thing as a world patent, so like anyone else they could never had that in the first place. If you cover the most important markets a lot is done though.
As for compound leverage mechanisms there are many different ones. It is highly unlikely they covered them all in the first place - for one there are normal compound pliers, scissors and various compound special tools available. Not to mention compound mechanisms used in machinery and mechanical devices. Their patent most likely covers a subset of compound leverage mechanisms well suited for folding or compact tools.
One reason other companies haven't been very interested in making one handed compound tools might be that it doesn't make much of a difference for many cut geometries? The SOG design have two main issues in that regard: 1. There is a limit to how wide a hand can grip (which is why most compound bolt cutters are for two hands and spread very wide), and 2. The plier fulcrum design is the same as for normal pliers.
So as a thought experiment imagine opening the plier to max hand grip width and put a round wire into the plier cutting jaws: Due to the 2:1 (or so) compound mechanism, and the hand grip width limit, the SOG plier will only open half as wide as the ordinary plier in the same hand. Thus the round wire will be about twice as long from the plier fulcrum compared to a wider opened normal plier. The grip force needed to cut depends on the distance from the fulcrum as well as the compound - so what is gained one place is largely lost at the other. (Though with more parallel plier cutters which is a benefit - as long as the round wire fits).
As for just gripping compound is great as long as it fits the narrower plier mouth.
« Last Edit: April 05, 2021, 07:17:31 PM by Vidar »
"Simple is hard"
(Partial disclosure: I design tools for a living).