I'm fine with all the civs included in Civ6 (although I'd still like to have some gaps filled), but if I were to replace one, this would be Scotland. Not only because there are better options for Celtic civilization (thankfully we already have Gaul), but I also find Scotland's design quite boring: Casus Belli, golf courses, amenities... meh.
Scotland is famous for its very beautiful castles, and there is nothing that references this in the game, maybe if the unique infrastructure was a castle or fortress instead of a golf course, I might like Scotland more. And Casus Belli-related abilities are always boring to me. Hopefully that Scotland will be balanced in April.
I wholeheartidly disagree with you. Except for Robert Bruce (who clearly seems out of touch with the rest of the civ), Scotland is wonderful for me. You say that their ability is "meh", but let's remember that Scotland one of the few science civs that don't rely on "flat bonuses" they'd get whatever they do if they're not too stupid (Korea). The way Scotland works and need to stay happy to become a scientific powerhouse is quite unique and it's probably, from all the scientific civs in the game, one of the best thought.
In this way, the Golf Course, while gimmicky, is truly Scottish and -best that, for example, Canada- synergizes perfectly with Scotland CUA.
The highlander... meh. But, to be honest, except if they have some very unique ability (like Canada's Mountee or Portugal's Nau), I don't factor UU to judge a civ, because I don't really care.
Also, you say that Scotland is famous for its very beautiful castles... First, I find that reducing Scotland to "beautiful castles", while there was beautiful castles pretty much everywhere, would be way more "meh" and not very "unique" in the sense that a castle is pretty much the most basic and representative monument for
all medieval Europe. Plus, France already have a castle of its own, so wouldn't it be redundant? At least, the Golf Course is 1) historical 2) visually unique and beautiful 3) synergize with Scotland civ ability 4) in a way, stray themselves from the stereotypical "Scottish castle" we might have. It has been a surprise, and we should have more surprises of this type.
Secondly, the Scottish Enlightment is, basically, what created the modern world. The proportions of discoveries, theories and inventions made by Scots is truly impressive. The only issue I have with this is that it's more a British than Scottish trait... But, if I had to choose between a British England and a British scotland, I'd choose Scotland and their Enlightment over the British Museum or Workshops of the World.
I mean, Canada is stereotipically gimmicky and people complain it's overly Canadian; Scotland is based upon historical elements, but not necessarily the first we thought of, and people complain it's not Scottish enough.
For me, Scotland (except Robert Bruce's ability (and the Highlander, but I'm part of people that consider 90% of unique units irrelevant)) has a brillant design. It's not the design at fault, it's merely its "legitimacy" in the game as yet another British civ in an already crowded Europe (I know talking about "legitimacy" is touchy, but I don't mean that Scotland is irrelevant, on the contrary, but that, in an overcrowded Europe, adding a second British civ seems overfeeding)