solved issues

Usually when the newly introduced bugs in the betas are mainly solved.

Each beta cycle runs for a quarter, so the current beta cycle will most likely be released as a non-beta during or at the end of next month (September).

I think it takes to long with so many solved bugs.

They should release more often. 

They could, of course, release software with fairly major and well-reported bugs. However, I expect that that would elicit complaints that they're releasing buggy software (heaven knows, it's bad enough already). 
Of course, if you're happy with that, there's nothing stopping you from joining the beta program. 

Just join the beta if you want access to the new features and bug fixes. But also be prepared to accept that sometimes things break.