140 champions
190 items
Different builds ( Trinity --> Steraks is going to yield different spikes than Steraks ---> Trinity for Frozen Mallet ---> Trinity )
Different timings (backs, jungle clears, etc.)
Different skill levels
Different "Meta's"
Hmm... I'm not trying to be mean, but can you really not figure this out for yourself? Like, really? I'll explain this super super super super simple.
More variables = Hard balance
Less variables = Easy balance
Just like in laboratory settings- the less variables you have in your experiment, the easier it is to consistently tell if your hypothesis is correct. That's why fighting games with less characters are far easier to balance, whereas fighting games with vast pools see clear tiers. It should not be surprising whatsoever, but you asked so there is your answer.