Sorry for the delay in the answer, but my time is limited and I even don´t know, if I can answer this all correctly in the short amount of time I have for it now. In any case, thank you very much for your Input.
In my eyes era 2 in CCM is a very interesting era, as it offers four different approaches to start into this era: You can start with "Engineering" or "Theology" or "Alchemy" or "Navigation". Each of these entries offers a different access to that era 2. Your start with "Alchemy" is only one of these multiple entries.
The start with "Alchemy" only makes sense, if you have a real chance to build the wonder "Philosopher´s Stone". On the other side a player who starts with the Tech "Engineering", than rushes a windmill in a productive City, can have a better chance to finish that wonder before you, if he aquires that tech or does that research as the second researched tech of that era.
The next step in the research you did, from Alchemy to Gunpowder is a "full risk step". Without the resource saltpeter, you gain next to nothing for your research (only a little better coastal ship) and on the other side you disable your Siege Workshop and stop your autoproduction of catapults and later trebuchets.
Now to the comparison between the "Late Pikeman" and the "Arquebusier". The "late Pikeman" has the same stats as the "Pikeman" of era 1, coming with Feudalism. The only - but important - difference is, that this unit doesn´t need access to a strategic resource.
Of course the states 2A, 4D are better than 1A, 3 D. But both units are defensive units and the late pikeman can be built in places where an arquebusier cannot been built and the unit is cheaper than the arquebusier. This can be very important in newly found cities that come under attack, especially when most units of that era have the option to pillage roads and therfore to cut off the supply of saltpeter or in newly found cities on islands. The difference between both units is, that sometimes you can build a late pikeman that can help you in the defense of a city, but you cannot build the arquebusier. So both units have their reason to be included in that time. For the offensive you have better units than late pikemen or arquebusiers in that era.
Now to the timeframe of the techs "Alchemy, Gunpowder, and Renaissance".
Here the first problem is that there are different understandings of the term "Renaissance". There is the "
Renaissance of the 12th century" and there is the the
Renaissance starting in Italy, that spanned the period roughly from the 14th to the 17th century.
Alchemy is a much older "tech".
The Wikipedia states: The introduction of alchemy to Latin Europe occurred on 11 February 1144, with the completion of Robert of Chester's translation of the Arabic Book of the Composition of Alchemy. Even without fixing that tech to that date, I think it can be stated, that Alchemy is an older tech than the "Italian Renaissance" (if the last one can be even called a tech).
The
arquebuse was introduced in the 15th century and therefore somewhere in the periode described above, the invention of
Gunpowder is older (invention in the 9th century in China and the earliest Western accounts of gunpowder appear in texts written by English philosopher Roger Bacon in the 13th century).
And now the real reason for doing the techtree of CCM in era 2 the way it is: Sandris made a lot of wonderful units and I wanted to have them all in my mod without enlarging era 2.
The first thing i did was click it out of curiosity, and i crashed an unsaved game 
. I was so into what i was doing i forgot to save 
