Yes, of course there should be a grid in Gutenberg. Its an integral part of any page building tool and the absence of it is the reason why I don't even try to use Gutenberg for clients websites.
Every single website i've ever built (over 200) needs some kind of layouting. Some need very minimal layouting, like 2/3/4 equal columns, other websites need much more advanced layouting like asymmetrical, overlapping and vertically justified columns.
So the grid system needs to be very flexible - but easy to use and understand.

If I were to design a solution for this, I would not make Gutenberg dependend on any existing CSS grid framework like Bootstrap.
I would instead introduce a new standard in the CSS classes used by the rows and column Blocks (like "wp-row", "wp-column", etc.) and make use of flexbox to design a very flexible grid system which does not rely on a certain number of columns. You could add an unlimited number of columns to each row and have the flexbox model take care of the rest, while providing settings on a per-row basis for finer adjustments like equal height columns, vertically aligning the content in each column, gap widths, negative offsets, etc.
This way, every theme would be compatible and it would be a very modern, futureproof solution, which enables users to build any kind of layout without adding the Wright of any dependency on frameworks to WordPress / Gutenberg.