The wardec mechanic, including the cost, was changed in 2012 so it is a bit of comparing apples and oranges. But over the course of the game, CCP has managed to keep inflation and the value of assets in a reasonable range:
Inflation doesn’t tell the whole story though as it has been kept in check by compensating for increased ISK in the game with increased assets - ISK buys you a similar amount but we all have more ISK and stuff. If you look at something like PLEX which may better reflect our in-game wealth, you’ll see it debuted in around 2008 for 300M ISK /month game time and is now around 1.5M ISK/month so a five-fold increase.
War costs haven’t changed since 2012, but then the minimum cost was raised around 25-fold from about 2M ISK to the current 50M ISK. But the costs pre-2012 were calculated differently depending on whether it was an alliance or a corp (alliances were still 50M I think?), and how many active wars there were. They also changed how quickly the war cost scaled with group size, shifting it towards increasing the cost for larger groups more quickly.
So I would be comfortable saying the cost of an entry-level war against a small corp has kept pace with inflation and is actually still more expensive now than when the mechanic was first introduced and was only 2M ISK. For alliances wars, given we have had only mild inflation, if not deflation depending on the index you choose, it is probably similar in terms of ISK value.
We are all richer though, so if you mean have wardec costs against alliances kept pace with how much wealth each of us have, then probably not. People can afford wars easier today than in 2012 and when the war mechanic was introduced at the beginning of the game just like they can afford everything more than in the past.
That is one of the side-effects of opening the ISK and resource faucets full-blast.