I don't think he's as nuts as you say, but I don't think he needs Relic Shield. I've looked at some Rakan players who are considered "Rakan Masters", and there's a trend. They're playing with a Xayah when they win, or they're playing in an uneven game when they win(one challenger on both sides with the other side having one master and 3 D1 and D2 players while their side has one challenger and all master players as one of the examples). There are some other occasions where they're playing with a Lucian and they win or someone else carries hard. Most of the games though they're all equal in kills(aside from Rakan cuz he's a support) with Rakan having like 11 or so assists, so I wouldn't say it was particularly Rakan who carried the game because of how OP he was, again, unless he's with a Xayah. These are master players btw.
The problem is how much he depends on Xayah to be as useful as he could, while Xayah doesn't depend on Rakan to be useful at all. This needs to be changed. Lover's Leap is a useful enough ability for them both, they don't need his E to be DOUBLE the range when dashing to Xayah, he needs a little more room to dash to other champions. They should change his E to where it's about 75% or 80% range for all champions with Xayah having no range buff imo.