Can you play dota2 vs bots
Yeah, you can. Play them to learn how to control yourself in the game, maybe find a hero you like, test out items and see what skills you will be facing. If you are looking to get into playing people, don't stay in bots too long. You're going to suck in matchmaking early, but there are a LOT of shitty people out there too.
I've seen many games in dota where it looks like it is snowballing one way and the other team is able to turn it around. Shit, watch almost any Na'Vi match at the I2 last year. I don't know how LoL is with regards to that, but Dota is far from a "well they got a couple kills early, frick it i'm out" kind of game. Though you will of course get those idiots.
Queuing up with randoms, yeah, you're going to have those games where someone feeds their arse off and it's tough to come back from. It's a team game, not a solo one.
That said, no one cheers in Dota2 when wards are killed. LoL has that.