I noticed it’s missing tab layouts present in vim.

I always found the tab bar in vim to be confusing. Does not out the box do what other editors use it for. So I am glad that it is missing from helix in that form. As for a tab bar that other editors use, well I guess vim already beat into me the need to not really use one. I do find that I don’t really miss it with all the ways to open files and select buffers in helix <space>b for instance to see and fuzzy search buffers is very nice (or <space>f for all files).

Also might it not be impossible to resize splits

Not yet it seems, though #1176 is tracking that and looks like someone implemented it a while ago. Might want to add your view to that issue to raise its importance.

There’s also no linewise selection mode.

X will extend the selection to full lines and x will also advance the selection by one line. I don’t think there will ever be a separate linewise selection mode due to how helix treats new lines. Though these keys are good enough for most situations.