Obviously, online poker is ALOT toughter. People playing online are just better poker players at average.
They much more often study, watch videos etc. They usually have more experience, since online poker is very fast, so they play much more
hands. Many of them are regular grinders, playing 6+ tables at the same time. They more often respect opening ranges, just because online poker is fast, they have no problem folding weak hands.
From the other hand, life casino poker player very often play strictly fo fun, just spending some time
gambling. Playing just one table they become bored, can't stand folding about 80% of hands like in "proper" poker it should be - so they limp/open/call with alot of nonsense, just giving away their money.
Life $1/2 or $1/3 cash games maybe can be comparable by level with online $0,01-0,02. If you try online $1-2 you are going to encounter 80% of pros/regs.