I don't think you need to worry so much about the popularity of
Theodore.
Today's popular names can't be compared to those that were popular in the past; the days of having five Michaels and three Jessicas in every class are pretty much over, I've seen the class lists. If you look at the data for
Theodore, it's the 7th most popular name in the USA, but the number of times it's been used is only 11,041 - in the ENTIRE United States, where 3.5 million babies were born in 2023. That's not many at all, if you think about it. If we compare when the name
Jennifer was the #7 name, in 1989, it was used nearly 24,000 times, twice as often as
Theodore is today. It's very possible that your
Theodore will be the only one in his class. So if you love it, don't feel you must give it up.
But, to play along, I'll suggest:
AmbrosePhineasDorianFeodorTudorHomerAlbertEugene