Changing the size of Gboard felt like I found the hidden cheat code TBQH. That being said once I found out how to resize the Gboard keyboard I find the customization equal to what I could do with the Samsung keyboard.I'd been using Samsung keyboard and switched to Gboard full-time a couple of weeks ago. I like the customization and effects with Samsung keyboard but Gboard is just much more accurate. I did find the size customization to be better with Samsung keyboard, but Gboard is great.
Good luck!