A single feat given to a character won't make the party OP. It'd only be noticeable for a party of fully custom characters with free feats (in particular GWM and Sharpshooter will be very powerful with Height/Backstab Advantage), and even then only for the first few levels. Past level ~3, character abilities+4th level ASI/feat would begin to eclipse this free feat.
If it turns out that this change does make combats at levels 2&3 too easy, then Larian can up the difficulty of these encounters. I assume they'll be making changes to their encounters up until release anyway. Fully Origin parties would probably find combats somewhat more difficult than fully custom parties, but I don't think it'd be that different. It'd be worth the additional customization that a 1st level feat grants.
