Well, I tried for a brief reply, and failed catastrophically! So this is a long but still info-centric reply - not my usual rambling, promise!
Here goes...
@Jake65 @JollyElf : The 2020 Combat Formula is universally applied in both the Spire (where it was first introduced, and which has always used it) and also, since August 2020, in Tournaments. It is not now and never has been relevant to World Map Province battles or Catering costs, which are now the only real purpose of knowing one's base / Barracks Squad Size, and which therefore become comparatively easier and cheaper as the game progresses and one's City becomes more powerful overall - although, of course, of much less importance to most players who have any interest in Squad Sizes/Catering costs in the Spire & Tournament. Even in Spire & Tourney, though, the City's base Squad Size is not
entirely irrelevant - because almost every City parameter forms part of the City Advancement Level, or CAL, which in turn is the base figure - varying between almost all Cities beyond the game's earliest stages - upon which the Formula's calculations, in their turn, operate.
The Combat Formula has no different type of effect upon any type of Enemy or player Troop Unit/Squad type combinations
per se.
As far as 'difficulty' goes - it's sometimes pointed out, and of course it's true in literal/mathematical terms, that larger Squad Sizes
alone don't increase the actual skill-related difficulty of the battles. However, many players, often including myself, generally use the term 'difficulty' to describe
the overall player effort required to produce the number of Troops and/or amount of Goods needed to sustain the increasing costs of Spire & Tournament Squad & Catering Sizes as each of those progresses each week as per the Formula's mechanics - which, in the end, will of course be fundamentally limited, as is everything in the game, by various core City factors [Supplies is a significant one]
and also the player's available online time - something which can be overlooked as a 'cost' of supporting high Spire/Tourney costs, but shouldn't be, in my opinion.
But the Formula itself doesn't vary weekly (or ever), nor
directly affect Combat difficulty in terms of "How much skill is needed to win any given battle?" - it affects only the Squad Sizes & rate of increase thereof, both on a week-to-week basis as one's City CAL alters (and typically grows, of course, as one improves one's City) and on a Province-by-Province basis in each Tourney, as well - and it therefore dictates the number of Troops needed and potentially lost, per battle per week - and also the Catering (or Diplomacy) costs, of course. For me, though using the shortcut term 'difficulty' - even if a bit controversial in some circumstances - is a near-universally-understood way of expressing all of this...!
And finally, as far as I'm aware, the make-up of Enemy Squad combinations in Spire & Tournament hasn't significantly altered ever since it was changed at the point when the Formula was introduced (well - there have been a few minor alterations to Spire combinations, notably to make them more likely, within the random generation of Enemy Squads, to feature a 3+2 type of arrangement whereby you'll often see 3
× x type of Enemy Unit plus 2
× y type - e.g. 3 x Mage plus 2 x Heavy Ranged, as an off-the-cuff [and a bit tricky!] example - rather than entirely random assortments, which are often more difficult to counter without losses).
For info : Inno certainly have been quietly experimenting with the Enemy Unit combos in the Tournament - I myself have, I am sure, seen at least two Tournaments in the past six months where my own Enemy Squad combos [and Terrain in some cases, too - interestingly] have radically departed from the post-2020 norm - but whether or not they will ever implement some, any, or all of those changes remains to be seen. On a purely selfish level, though, as a Manual Combat player who likes to use all my available Troop types if I can, I hope so - assuming that the two non-standard Tourneys I personally saw were any guide. Not only were the Enemy Squad combos easier to deal with for Manual Combat players (and perhaps Auto-Combat, too? - not least because the AI finally seems to be being revised to account for ALL player Troop types, not only specifically 3* Merc Camp Units, which in my experience are the only type which it understands and assumes players & AI will both use)... but who can say, where companies use silent unannounced tests rather than the boring old traditional open Beta testing route?
My most current info on which Enemy Units will be seen in any given Tourney type (and the Spire tends to follow a similar weekly pattern, too, albeit with more randomness) remains pretty reliable, and is shown in the chart below - which was produced by a Beta player called Dony. He is (was? - hasn't been seen for over a year...) arguably one of the game's foremost Combat experts (and certainly one of its most studious and active followers, mathematical analysts & bug-reporters, and practitioners, with much Beta content and even YouTube strategy videos to show for it).
Here is
Dony's YouTube Channel (NOT affiliated with InnoGames) - hey, why not watch a
real expert fight with Squad Sizes of up to 100K !!
Dony produced this chart when the 2020 Formula was introduced, which is the point when the Tournament Enemy Squad composition was changed - and when some of the Map Province Units were removed entirely from Tournaments. I have seen no further info about this, and my in-game observations show that, outside of Inno's silent A/B testing of recent months, they are still using the same predominant Unit combos shown (within the always-random generation of Enemy Squad types)... and may well continue to do so, for all I know as a mere player!
EMPHASIS : As stated, the varying weekly Enemy Squad combinations are somewhat randomised, but the chart below is at least a good guide.
Here: you go: