This dovetails with my own experience more or less exactly: when I launched my company, it was easy to throw everything on Heroku, and to their credit and detriment it was also fairly easy to move pretty much everything _off_ of Heroku (RDS for a database, RedisLabs for, well, Redis, and so on.)
Two years later, though... the inclination has ebbed. Heroku hasn't shipped anything meaningful for my use case in the past 24 months, but also they have been fairly stable. I'm sure I will migrate off of them onto something else in the fullness of time, but it would take a pretty severe precipitating event.
Back in 2021 (https://news.ycombinator.com/item?id=29648325, https://news.ycombinator.com/item?id=30177907) and 2022 (https://news.ycombinator.com/item?id=32608734) Heroku went from "well this is costing enough that it probably makes sense to divest at some point and save the $X00/mo" to "Heroku is now the biggest systemic risk to uptime that I have", and it felt _very_ high-priority to get off of them and onto someone else.
Two years later, though... the inclination has ebbed. Heroku hasn't shipped anything meaningful for my use case in the past 24 months, but also they have been fairly stable. I'm sure I will migrate off of them onto something else in the fullness of time, but it would take a pretty severe precipitating event.