>jazz comes in two distinct forms
As you can see from the replies, you made a basic mistake with this comment.
There is not two forms of Jazz, there are many forms, in the same way there are many forms of "pop" music.
Music that you call Trad (Traditional) mainly came out of New Orleans between about 1890 and 1920. This was played by Louis Armstrong, King Oliver and others. I suppose you may call it "good time" music.
But then it evolved into other styles like "big band" (30s and 40s) with Count Basie, Benny Goodman etc
Then Be bop (1950s) with Charlie Parker and Dizzy Gillespie. I guess this was the start of Modern Jazz, but it was still tuneful.
In the late 1950s early 1960s there was a revival of the trad jazz when people like Acker Bilk, Kenny Ball, Chris Barber and so on played the good time music from the 1920s.
There was a free-form style in the 1960 and 70s, but it was only one minor style of jazz which only had a specialist following.