Yes, in 2004 we were very strong honestly, for example we had Zikos who played the full 90 mins of the Champions League final that year and didn't even get called up for the tournament because we had other better players. Also, back then the Greek league was much stronger than it is now, we had 3 clubs in the Champions League group stages that year for example, in addition to many other players at top European clubs (Karagounis-Inter Milan, Nikolaidis-Atletico Madrid, Dellas-Roma, Fyssas-Benfica, etc).
2006 we had a tough group also (no massive teams but a lot of solid teams and depth) and just missed out on the World Cup. We had Ukraine, Denmark, Turkey, plus Albania who historically don't like us so they had extra motivation against us.
2008 to 2014 we were good and very consistent, we qualified for everything and almost always beat the teams we were supposed to beat, but rarely pulled off upset wins.
After 2014 we were pretty much in shambles, for a number of reasons I won't get into, but some of our results did not make sense because we had many players at top European clubs who consistently did well on a club level but when they all came together for the national team, we were horrible. On paper we had arguably a much stronger team than 2008 to 2014 but just could not get results. For example Sokratis, Manolas, Mitroglou, Samaris, Holebas, Torosidis, and K. Papadopoulos and Karnezis to a lesser extent. We still almost qualified for the 2018 World Cup but otherwise our results were very poor.
Now we seem to be doing well, even before Jovanovic we showed some good signs and came third in a very tough group for Euro 2024 qualifiers and had one bad game against Georgia (in which we still didn't concede any goals) which ruined our chances but after the first three Nations League games, I think it's time for us to finally believe in our national team again.