I don't care what a bunch of people who pirate games have to say,. In general, the Western FE fanbase usually just cares about how overpowered a lord is (in comparison to the Japanese fanbase, there are some that actually disdain for that, and some want to see the power of lords toned down back to pre-FE7 levels). Prior to FE7, lords were more often than not "weak" or "mediocre". Heck, when Shouzou Kaga (the creator of FE) left IS and made Tear Ring Saga, Ronan (the lord of Tear Ring Saga) was weaker than any other lord in the FE series, except possibly FE1 Marth. Reese from Berwick Saga, I heard was even weaker than Ronan.
Secondly, they are right that Eliwood is better as an unit than Lyn (especially on Hector mode).
However, within the context of FE6, Roy is among the best units in his game, though he is definitely among the weaker lords in the series (he is better than Leaf and FE1 Marth, and probably on par with FE3 Book 1 Marth and Micaiah). Roy is not terrible early game, and is probably better than most other units in the early part of the game with the exception of Alan, Lance, Dieck, and Rutger (who in general are amongst the best units overall for FE6).
Roy's main handicap overall for FE6 is his absurdly late promotion. Had he promoted at say, Chapter 16 (where he becomes leader of the Etrurian Army), he would be considered among the Top 5 best units in FE6. As he is currently in FE6, he is regarded among the Top 10 best units in that.