Personally I think leather jackets worn by airline pilots can look somewhat sloppy at times, but it's just my humble opinion.
The silliest thing in modern terms, as far as silly goes in a pilot's uniform, has to be the hat however.
And, as traditional airline uniforms go, they get their 'professional' reference from the Navy skipper uniforms and professional nautical shipping business from the days of olde. The hat, the stripes, the jacket, the brass pomp and circumstance - it's all very Captain Stubing or SS Titanic.
Professional pilots were first called 'Chaeuffers' by the way, until they adopted their rightful nautical 'aire' and it probably had a lot to do with the fact that they took over where the oceanliners left off.
I flew for one of the first major airlines that allowed leather jackets, bought one, wore it, etc. Southwest got them. Then all the commuter airlines got them. Then United, and the list goes on now as it's a fad.
Internationally speaking, in most places outside of familiar northern cultures/climates we are used to, a leather jacket would not only be so hot it would be unbearable but would also look very odd. When there are language and cultural barriers in place, the silly hat that looks like a Goose parked on your head and the pompus coat and brass do a lot to get you sped through all the other 'official' looking guys with big hats and plenty of time to make your day very delayed.