Indeed, it is on pure luck. Sometimes, a single spin can land to a bonus round, and sometimes even with 200 or more spin can't land you a single bonus round. I had experienced them both. And what funny is even if we are lucky enough to get a bonus round, we are still unsure whether that bonus round can give us a multiplier. There are times that I won't hit a single win in a bonus round after hundreds of spin to get into it.
It's the craziest part, when you wait that bonus bet after bet, bankroll is going down like crazy, and when you finally land on it, you get literally nothing, some funny & low payout! Been there many times!
Slots! Who plays them knows how crazy they can be, crazy good and crazy bad! It's why slots should be played only with money you can lose and not get emotional over that loss!
Slots are purely luck based, dice is purely luck based, plinko is lucked based we can continue to talk about what we can and at the end of the day we are not going to suddenly have games where being smart could mean you could make a profit, there is no way for that and it is mathematically impossible for you to win in the long term. So basically, all games are luck based and slot is not an exception to it.
The thing about slots is that you have a million of them and some of them are gamble a lot and win once to profit big, and some of them gamble some and make almost all back each time losing slowly, like there are all kinds of different slots.