Maybe it escaped you, but he didn't stay in RW. He drifted to whatever the feck he wanted; even in some cases to the left wing. He's more of SS/AM/free role than RW in all the games.
Lingard is a player who relies on making the right runs at the right time - him drifting about from the RW is different to him playing directly behind the striker as a player who reactively makes the right move & run - whilst also having a good shot on him.
Best example is how Lampard was so deadly behind Drogba - the latter created so much space for him that Lampard was at the right space & the right time to play off him & score the goals literally off Drogbas hard work.
Lampard would be hindered if he was asked to play as a RW - even if he had the freedom to move where he wants - be it keep the width or cut in, he would not consistently be directly behind the striker playing reactively off him.
Lukaku helped Lingard more than any other player because there was space off him. It was the first games that Lingard actually got to play in his position consistently & he did well. It was something a lot of fans were surprised about last season - but it was always going to work because he is a very direct player & needs to play in a direct position.
Give him a run of consistent games off any striker as a SS/Cam & he will be better positioned than being told to start out right & drift anywhere he likes from that position. Lingard at that point becomes a supplier to Lukaku more than a forward off Lukaku.
Remember how he played wonderful just off Rashford in the 352 against Chelsea? Absolutely class.
Martial, Rashford, Lukaku Sanchez & Lingard are all forwards - we need to stop using one; if we get LF, RF & False 9 - it will be obvious to a lot of us at how different the forwards capabilities are & this would lead us to actually having some cohesion for once.
Imagine Rashford & Lukaku upfront with the central spaces open for Martial as a false 9 to take his men on & shift the ball left & right. Imagine Lingard being a more direct option to Martial - play Lingard as a False 9, with Sanchez & Rashford playing off him - the sheer tenacity between those players would be hell.
The list is endless. Positioning means a lot & a lot of our players are not positioned well. Lingard was last season at least better than normal or what I have seen this season.