I've started to play around 18 years ago and I can say that definitely
online poker is more difficult now. But the main reason for me is the lack of options we have now and way less players than it used to be. A lot of countries can't play in the big rooms anymore, specially US players, which were the biggest market for online poker. After Black Friday in 2011, almost all poker rooms have closed. We only have like 4-5 poker rooms that we can trust, so, all players have to play in one of them, so, the competition is tougher.
In the past, we had like 15 (or more) good rooms. So, I remember that most of the good (and professionals) players used to play on PS or Full Tilt. But if you were not that good (like me..lol), you would still have a lot of good rooms with weaker players to choose. That time you could easily win a decent amount of money, nowadays I think only the very good players can win.