I never proposed that the Constitution should be easier to change. For the past 30 years, there have been no changes to the constitution. In the 1900's, there were 11 amendments. That's an average of 9 years per change. I refuse to believe that in the last 31 years, there was nothing important that 75% of States could agree on. The world has changed a lot in that time because of the internet and other technology. There's definitely a lot of new things that there could be amendments about.
An example would be an amendment on privacy and data collection. Over 80% of americans feel very little or no control over data that is collected about them. 81% feel the risks of companies collecting data about them outweigh the benefits. Source of data: pew research.
There's definitely room for an amendment there. It doesn't matter how smart the founders were, the world changes and the constitution has to change to reflect those changes.
The number of languages one knows doesn't make them the best, most educated of a generation. I say this as someone who can speak, read, and write 4 languages. I can also speak, but not read or write another language for a total of 5 languages.
For someone who puts so much weight into how educated the founding fathers were, you seem to disregard the educated people of the generations currently alive. A key difference between humans and other animals is that we build upon the knowledge that previous generations discovered by writing down what we learned and teaching it to future generations. Not only do we build upon previous knowledge, but we have also made knowledge more accessible through technology. The most knowledgeable of today's generations are smarter than those of generations centuries ago.
You say the founding fathers studied ancient greek and roman governments. Modern political scientists study that too. They also study our government and what has and hasn't worked well for it since it's founding. They study what other governments are doing in this new world and how it's going for them.