Harry doesn't need to wear the Goblin suit because he is not trying to be the Green Goblin. It's as simple as that, people. His goal is to avenge his father by destroying Peter/Spider-man, and his father's technology is providing him with the means to do so.
That's it. He won't be parading around attacking innocent people. Harry is going after Peter. The only reason he's being called the New Goblin is simply because of the similarities in technology between him and Norman, and I'm willing to bet that he's given that name by the Bugle. Even in the footage we've seen with Harry talking to "Norman". We see Normal telling him, "Avenge me." He doesn't go, "BECOME THE GREEN GOBLIN AS I DID!" Yes, this is different from the comics, but that doesn't mean it's bad.
Harry is not wearing his father's suit. And the only reason we have toys of the original Goblin is because they are creating an extensive villain lineup, with Kraven, Rhino, and others. So everyone needs to chill on this.