All the OEMs think they have the best answer to wing design. And every wing is a compromise. Until recently I did not realize there are three wings on any airplane.
1) there is the jig wing which is the wing that is built and not attached
2) there is the ground wing which is the jig wing attached to the airplane and thus subject to the effects of loading, environment, etc
3) and then there is the air-wing which is subject to all the previous plus the various aero-loads at different speeds. Of course, this air-wing changes as the various factors change (weight, speed, load, etc)
Winglets change the aspect ratio of the wing just like lengthening the wing does but there are tradeoffs. You are working at the weakest point of the wing and you are asking the wing tip to bear a greater load during flight. Obviously you will have to design the winglet for a specific regime to make it worthwhile. And in doing so, IF the winglet is after-market, you are essentially creating a NEW wing, not just bolting on a angular bit of metal.
Boeing intially offered the 777 with folding wingtips but it came with additional weight and complexity. No one wanted it. And now various groups are looking at aftermarket winglets for the 777.
Raked wingtips can offer many of the benefits of a winglet but they don't offer ALL the benefits.
Interesting thing is winglets were considered BEFORE Orville and Wilbur flew. Then they were called wingplates and they worked to diminish the vortex at the end of the wing.
You can still see wingplates today but they are on racecars where the aspect ratio is not a consideration but rather an effective wing that creates down-lift with reduced drag to pin the race car to the asphalt.