What do you mean by "the tech tree ends before Tanks"?
I'm pretty sure he meant most of his games end when no one including him has gone through the modern era techs, the bottom of the tree anyway. Quite a few Prince players have complained about either this, some have even reported it as "a bug", or about the AI falling so much behind it's ridiculous (eg: all of them end up two full eras behind the human by Modern).
I played my first two BNW games on Prince to get a feel of the new features and I indeed found it slow, if not quite as slow as Horizons and others have described (I played on Immortal/Emperor on G&K, so I rather had the super-runaway human, super backward AI situation). On the King games I played before getting back to Emperor, I noticed it's already much better balanced, if still slower than pre-BNW and post-BNW on Emperor and above. But it's only back on Emperor that I really started to experience how the tourism/ideology systems were really designed to work, the TR from science etc. It's like King is the new Prince - with the new mechanics and a bit of advice to optimize the growth/science aspect of your game it's now easier to perform well on King and definitely more fun to do it on King than Prince, without the problem of the AI falling so much behind and giving you really boring games (unless you're satisfied with running away and playing in your sandbox toward the victory of your choice).
IMO, that might be a side effect of the new mechanics. On Prince players (human and AI) have zero science benefits from early Trade Route, so they go through Ancient and Classical eras much slower than it's done on higher levels, where the science lead of the AI carries you along (having saved you tons of research turns by the mid-game, while the AI also kept up). Depriving one of the AI of the GL seems to reduce the odds even one AI can become a runaway (and thus of at least one target for spying, and for RA, and beakers from TR), so the human takes a science lead very early in turn #, but by doing so to advance in the tree he must rely exclusively on his own beaker production (and occasional GS) for the rest of the game. The average human player also has little hope of stealing techs on Prince, by Renaissance there's very few ever available unless you follow the strategy of teching up the tree to let the AI research the bottom first, and even then.. it's so backward it's not that great an idea), and RAs are more than worthless on Prince (which doesn't stop the AI from spending its gold on that). None of this helps the Prince players advance fast in science, and rapidly their game fall behind the "historical times" (ie: they get Riflemen in the 1900s, tanks barely start to appear by the endgame etc.). It seems frequent on Prince that by the endgame (early by diplo win, or a bit later by culture, or even Time) many of the AIs have not yet picked an Ideology.
Other factors that don't seem to help are that the AI on Prince can't expand as much, because it doesn't have the extra happiness for it. It plays with much fewer cities, but not necessarily following a good tall-tradition strat but going Liberty or Honor (and as a side effect, on large maps this means games in which the warmonger penalties will be
very steep: not enough cities for each AI, not enough cities settled on the map until very, very late game = much higher penalties than on higher levels where the large map is full by mid-game). None of that helps the AI much with its science Culture-wise, the AI can't have many buildings for GW, for lack of cities, and on Prince it's almost a fluke that it gets Wonders, so in most games the AI has low tourism, which trivializes the whole Ideology system (it's easy to win it even without the Internet) and the teching is so slow it's normal the game ends with a few AI not even having picked an Ideology. All that also means the AI runs out of options to increase its happiness: no Wonders, few cities = few buildings plus it techs too slowly to get the late game ones, the player also doesn't let it keep CS allies for long.
Horizons seems to describe the type of Prince game played very casually without an emphasis on growth, with early bulbing of GS to needlessly start building Wonders you're certain to bag anyway - neglecting getting those 3 academies for the capital - or else too few Specialists, or the wrong ones, assigned. Also, opening Rationalism too late, not having enough early CS allies or neglecting to adopt Scholasticism, etc. Not playing a
great sandbox science game on Prince seems to result in those ultra-slow science Prince games post-patch.
OTOH, Prince players who adopt the growth-science emphasis do keep up (ie: in reaching techs earlier, if not as fast as on the highest levels) but for lack of any AI competition they become totally overpowered by the Renaissance and have boring, slow or sandbox endgames.