I used postgres in the 90s. The biggest complaint was that postgres's default config needed a change so you could connect to it remotely, as the default, wisely at the time, decided that allowing connections from any IP by default before you changed any security setting whatsoever was a real problem.
The MySQL performance advantages were large, with the small caveat that it was fast as long as you were using MyISAM, which achieved its speed by throwing away many safety features, like working transactions and foreign key constraints. Unsurprisingly, when eventually it got an engine that didn't throw caution to the wind, the performance advantage went away.
I spent a lot of time in the early 2000s showing people whose that many of the issues they were facing with their e-commerce websites were ultimately down to the MySQL engine they had picked. But it's faster! Yes it is, but now your application code has to deal with all the things the engine has now offloaded to your application code.
It's not that Postgres' changes were key to increasing market share, but that as MySQL matured, it had no options but to lose its 'advantages'.
That mirrors my experience. MySQL was faster for use cases where data loss was acceptable. Will anyone die if you lose some web log analysis stats? Probably not. You wouldn’t want to use it for anything where guaranteed consistency was critical, like anything involving money, but it was an alright replacement for things like an in-memory data store.
If you want a fast DB for web log analysis, you shouldn't look at MySQL or PostgreSQL anyway. ClickHouse will run circles around both of them for the use case of web log analysis.
That was an example of the sort of thing that someone might reasonably have used MySQL+MyISAM for in the past. I wouldn’t use that combination at all today.
The MySQL performance advantages were large, with the small caveat that it was fast as long as you were using MyISAM, which achieved its speed by throwing away many safety features, like working transactions and foreign key constraints. Unsurprisingly, when eventually it got an engine that didn't throw caution to the wind, the performance advantage went away.
I spent a lot of time in the early 2000s showing people whose that many of the issues they were facing with their e-commerce websites were ultimately down to the MySQL engine they had picked. But it's faster! Yes it is, but now your application code has to deal with all the things the engine has now offloaded to your application code.
It's not that Postgres' changes were key to increasing market share, but that as MySQL matured, it had no options but to lose its 'advantages'.