Popularity != value. Also, this thread seems to focus on just the SM era onward, and mostly on individual cards instead of as a whole. And also mostly on the western side of the world, since Greninja and Buzzwole have had a very popular period in Japan where they were more popular than some of the other mentioned Pokémon for halve a year. 
Popularity simply isn’t something that can be measured easy, since there are so many factors to consider, and it also changes day-by-day.
Anyway, to contribute something (do with it what you will), focusing on just value of the highest single card sold for that specific Pokémon, the order would be:
- Charizard (PSA-10 1st ed. Base Set sold for 420k USD in 2022)
- Blastoise (Protostoise sold for 360k USD in 2021)
- Pikachu (SNAP ungraded sold for 270k USD in 2023)
- Umbreon (Japanese PSA-10 Play GS sold for 180k USD in 2024)
- Kangaskhan (PSA-10 sold for 175k USD in 2023)
- Lugia (PSA-10 1st edition Neo Gensis sold for 144.3k USD in 2021)
- Magikarp (SNAP ungraded sold for 136k USD in 2022)
- ?? Gyarados (SNAP ungraded sold for 87.5 USD in 2023)
- ??
- ??
Also, I personally think Eevee is way more popular than Umbreon, even if prices don’t reflect that. Mostly because one is usually released as Common and the other as SR, making focusing on only value a weird way to measure popularity imo. 
Greetz,
Quuador