An article by Rachel Andrew has this to say about the above question in the context of using the new CSS Grid capability:
If your website really needs to look the same in all browsers (whatever that means to you), you won’t be able to use any features only available by using Grid. In that case don’t use Grid Layout! Use Grid Layout if you want to achieve something that you can’t do in a good way with older technologies. Then create a fallback that gives a good experience to those less capable browsers rather than worrying about making it exactly the same. The power of Grid is that we can do things that were pretty much impossible before. Use Grid for that, not just to replicate your old design.
We tend to agree.