It's a bit of a problem with wider strats. Even with the ideology happiness-tenets, you may find that its a fairly nasty surprise. I was playing as a rather wide (and growing) Russia that had started off with Liberty and was heading for world domination. Because I took Autocracy (for Clausewitz' Legacy, which I got after totally eliminating my first victim), I ended up having a devil of a time even with Stadiums in a handful of cities. I took the first-tier tenets for happiness from military structures and defensive structures and started spamming walls-castles and barracks-armories-military academies just to break even. Only once I added the happiness boost to courthouses was I safe from going into -10 happiness or more with every city I conquered. Bear in mind, this was all even with a decent number of stadiums already up.
I think it's a sizable penalty, for stadiums to provide less happiness, in regards to wide civs. Luckily, I got to ideologies fairly quickly in my game as Russia; I can't imagine what would have happened had I somehow not had coal, because I rushed 3 factories for the ideology.
In a worst-case scenario, one might find no coal and not be able to trade for it for one reason or another, and in that case, it's a long wait until the Modern Era for ideologies. Which is why I do think nerfing stadiums that much is an issue. Also bear in mind, there is now no SP in Rationalism that provides happiness. So, all things considered, happiness in the latter half of the game is now harder to come by, significantly so if you don't get an ideology right away via the 3 factories...