How on earth Siam is three tiers above Sweden I cannot understand. Sweden likely brings in much more from city states than Siam does because they actually have the ability to gain the alliances with little to no effort in the first place.
Siam's ability is mediocre, while the other uniques are quite nice. However Sweden has a powerful ability with one relatively powerful UU (Caroleon) and one irrelevant UU (Hakkepalliita).
Sweden's 10% GP generation for DoFs is also powerful and not hard to utilise. The two sections of the UA give Sweden a lot of versitility. Not only can Sweden, unlike any other civ, choose between tourism and CS influence on their cultural great people, but they can also choose between whether to play a peaceful game and generate scientists somewhere in the vicinity of 20-50% faster, or to play an aggressive game supported by a good UU in the Caroleon and the ability to get CS on their side by gifting away their Great Generals.
For me Sweden is upper tier, while Siam is somewhere between middle and upper-middle. I'm bewildered by the fact that they are considered Lower-Middle, along with Greece, when those are the only two civs that can be guaranteed to be compete for CS on deity without either going Patronage or being Venice (and therefore not being able to settle cities of course, a pretty significant opportunity cost).
Portugal, another diplomacy based civ, is also above Sweden and Greece despite having a mediocre ability, a mediocre UU and a somewhat good but awkward to utilise UI.
There are a few other placements strongly I disagree with, but this one stood out like a sore thumb. I must be missing something about Siam if they apparently "are guaranteed to have good starts and/or can salvage bad ones", same goes for Austria to a lesser extent.
Still, a pretty good tier list, I'll enjoy reading more of the discussion in this thread and look forward to hearing your counter arguments