Ferrari had a good car (very good in fact) at points throughout the 2017 and 2018 seasons, just Mercedes excelled at developing the car (the 2018 Ferrari was a match for the Mercedes for the most part, till they brought their ‘upgrade’ at Singapore and Mercedes stretched their lead from there till Ferrari reverted to an older spec) and general team work in race strategy, pit stops etc. 2017 was probably their best chance, one big mistake in Singapore and reliability kind of put a dampener on a Vettel WDC bid though. Vettel did have the hand over Raikkonen (and would have done even without Ferrari’s very questionable strategies for Kimi) over both seasons though.
I think whether the Aston Martin seat is a good one going forward or not depends on what happens with Renault’s protest, If they’re given the all clear (like they were before the season started) then its definitely one of the best seats for next year and currently 2022 is a bit of a gamble for most teams, Alonso has already said he’s banking on Renault nailing the 2022 reg change and told them not to focus on 2021 already. It could be a fantastic move for Vettel though, certainly lower pressured than the Ferrari seat which can only be good, Mercedes and McLaren of late are a prime example of this being a key factor to doing well in my opinion and Mercedes especially where they say they have a no blame culture and they win and lose as a team, Ferrari is the complete opposite. Ferrari sometimes win as a team and when they lose they look to which person to cut loose
Wherever Vettel ends up I just hope we see a bit of a resurgence from him.