When I started out I played 10+0 (which was blitz back then) and 30+0. 30+0 was a lot easier at those early ranks but far too many people was running out the clock to make it fun to play that time control. It was also rare that i ran out of time playing 10+0 so it made no sense to play longer time controls.
Around 1500 rating i had to switch from 10+0 to 15+10 because i lost way too many winning positions due to time problems. What I immediately noticed was that the tricks and traps I could use to win at 10+0 simply didn't work at 15+10, people had enough time to figure out a solution if my play was flawed. Wins on time were from winning or tricky equal positions, losses on time was due to thinking too much from bad positions.
it might have changed now, i just came back to this site after a 2.5 year hiatus where i focused on other stuff.
That being said, I do believe there is a difference of skill level between 3+0 and 5+0 within the blitz pools. 5+0 feels easier than 3+0. Others have said something similar. It’d be cool to have data on ‘performance ratings’ between different time controls within the same category.