They really need to put an extra tier in the tech tree between Factories and Railroads/Electricity/Combustion
perhaps Future Tech can be researched in the same Tier as Rocketry (ie Rocketry is for the Science win, everyone else goes straight to Future Tech instead)
Right now, the Modern Age Tech Tree has 6 'Tiers' in an Age that nominally runs from 1750 to about 1960 (first humans in space, roughly), or about 210 years, or 35 years between each Tier of Tech.
The problem with that nice, linear picture is that it would mean that the first 4 Tiers of Tech would all be 19th century and the last Tier would be about 1925 - 1930 and so would have all the modern aircraft, battleships, tanks, rocket boosters et al stuffed into it - and almost no one would ever get a chance to play with them, because the game would be over by then.
All of which simply means that the time between Tech Tiers has to be really elastic to give people any time to play with the modern stuff, but also needs to provide enough 'room' for the 19th century developments of Industrialization and application of steam power to railroads, factories, shipping and warships.
Unfortunately, as applied in the game at present, the Tech Tree virtually skips the firs 100 years of the Age: Steam Engine is in the first Tech Tier, and it gives you Ironclads - the first of which was not launched until 1859, or 109 years after the Age starts.
Tier Two includes Techs giving the gamer the Dreadnaught and Landship, both developments from 1906 - 1916, or 46 - 56 years after the Ironclad, and skipping completely all the pre-dreadnaught naval developments of steam frigates, steam-assisted ships of the line and the first battleships. The Rail Station and railroads also appear in this Tier, making railroads about 70 - 80 years later than they appeared in reality.
Tier Three includes the first aircraft, which in fact appeared at about the same time as the Dreadnaught and Landship (1906 - 1916). This Tier also has the Eifel Tower Wonder, but since that was built 35 years earlier, either the aircraft or the Wonder are Very out of place.
Tier 4 has the Mobilization Tech, which gives you the Battleship, Destroyer, Submarine, and Aircraft Carrier: four ship-types that appeared, respectively, in 1915, 1894, 1901 and 1918 - 1925 (depending on whether you place the aircraft carrier when they first ships were built or when they first got effective ship-carried aircraft like torpedo and dive bombers). In the same Tier is also Armor with a collection of tanks and artillery that date to no earlier than 1932 (antitank guns) but mostly around 1940 (the medium tanks and self-propelled heavy artillery). In short, another Tier that covers almost half a century.
Finally, Tier 5 has the modern monoplane aircraft, even though in fact they were developed at about the same time as the medium tanks and artillery of the previous Tier - 1936 to 1941.
Tier 6 is basically all the rockets and craft necessary for the Launch Science Victory and practically nothing else.
This is a quick overview, but even from this it is obvious that the Modern Age Tech Tree is a mess that slides past half the Age and then presents units and developments completely out of sequence as it careens towards a Science Victory Only last Tech.
At the very least, a revision needs to place railroad development much earlier, place all the WWI developments in the same Tier and all the WWII developments in the same Tier. My Landships should not be crawling about the map for many turns before the first Biplane appears overhead, nor should medium tanks and self-propelled heavy artillery be thundering about long before the first monoplanes take flight.
