Why is 1815 the logical switchover point between EU and Vicky? EU3 ends in 1820 and Vic2 beginns in 1836!
The industrial revolution didn't take off outside of Britain untill the later half of the 19th century. Britain is a juggernaut from the get go and that is why Vic2, as it is today, is extremely unbalanced. If you beginn Vic2 around 1871, then the other powers have caught up with Britain. This rarely happens in Vic2, if the game is played from 1836. Britain can quite easily keep most other Great Powers behind it throughout the game, cause it starts of too superior (as the UK was IRL in 1836).
The USA is too powerfull globally in AHD, it even dwarfs Prussia from the start. Prussia had the most powerfull and advanced military IRL during the later half of the 18th century. Prussia fought three quick and very succesfull wars (1864, 1866 and 1871), if seen from a Prussian perspective. This makes the American Civil War a very bad scenario (in Vic2), because the Confederates looses too quickly and the americans quickly becomes a juggernaut like the UK. Leaving France, Prussia (Germany), Russia and the other potential GPs far behind them.
Ironclads, machine guns and other new terrifying inventions of the industrial revolutions, didn't really make an impact untill late in the 1860'ies. The monitors of the Civil War could be advanced galleys in EU4, as they where quite incapable of oceanic voyages. The first Ironclads, some where even ordrered by the CSA, but they where not available before the CSA had surrendered to the USA. No need to portray industrial revolution in EU4, as the military units of the the pre-1870 era weren't industrialized yet. War ships of the 1860'ies were still well known concepts such as: ships of the line, frigates (some had iron plates attached to their hull in the later half 1860'ies) and clipper transports. The three branches of the armies were also still: infantry, cavalry and artillery.