Totally agree with you, it is never a bad time to invest in coins like bitcoin and ethereum if you are planning to invest for a long time holding purpose.
But yes for short term, ethereum has just rose so It would be much better to wait a bit for it to dip again and then buy some of those.
Are you sure that Ethereum will go down in the near future? because according to news from several people that tomorrow there will be a London hard fork on Ethereum and everyone predicts that Ethereum will continue to rise in price.
that's part of the news that many people will wait for the process to take place in the market. whether it will have an impact or not. what is certain is that the large ethereum community has been waiting for this big update for a long time.
just pray this situation will make a decent improvement to the ethereum state. because of the issue of transaction fees that are always discussed, of course, this can be one of the focuses of the update.