Its been a while since I read the book, but I dont actually recall the kids in the book ever wanting to go near Pennywise or finding him funny so why does Pennywise need to look like a friendly inviting clown?
As for the design, aside from the yellow eyes (which are blue and normal when he isnt in murder mode) and the general creepiness of every clown ever, what is so frightening or evil about the design of this version of Pennywise? The goofy hair, the exagerated receding hairline, the gigantic bulbous forehead, the laughable victorian era clown outfit, buck teeth...? Those things arent really "evil" traits. Those are standard clown aesthetics.
People keep saying this version Pennywise is too evil looking but when he isnt in murder mode and popping out and glowering creepily in the dark he just looks like a clown. Not an evil clown. Just a weird clown. Stop thinking of this design in the context of the creepy scenes we've scene in the trailers. Scenes in which he is meant to be scary and meant to frighten the kids. Think of this design purely in its own terms in a normal environment like at a sunlit fair. What is too evil about this design?