Hi,
The submit button is not mandatory. You can hide it with CSS if you don't want it. For example, by adding such CSS:
.hikashop_checkout_payment_submit{ display: none; }
And yes, we specifically kept the old checkout as an option for people who would prefer the old checkout.
Please understand that the new checkout is a really big change for us and not everything could be iron out as well as the old checkout on which we spent 7 years perfecting. We need feedbacks like yours and time to be able to implement improvements.
This new checkout is just a new strong base on which we'll be able to build upon in order to go further in the future.