Easier to Play New Champs

Ok, as a person who's been very tight on money for various of reason, but has time to play the game, I, as of many, don't get as much out of the game as some. Now skins and summoner Icon, I don't have a problem with not owning, but I like to try and get new champions to play. Now it is a good idea to have influence points to get to the champs, but the problem is, it takes forever to get the champs you want, like for instance, your champ costs 4800 or 6300 Ip. But once you get that champ, you may end up disappointed in said champ. Now I understand, that's what free rotation is mostly for, but my question is, Riot, how come there isn't a game mode, where all champs are accessible? Now, allow me to explain. I'm talking about a game mode where every champ is accessible, to allow a person to get a feel of the champ, to see if that's what they want. Because otherwise, you're stuck with the current champions, plus free rotation. And then you have to wait when your or , comes into, or back into rotation, which could take weeks, if not months. Making it very susceptible to purchase blindly. So why can't there be a game mode with no mastery points increase, no ip increase, or anything, just a chance to play characters you don't own. I don't see how it would affect profits too much, after all, people are still buying riot points for skins and champions. It would be like a training mode that would of benefit you in knowing how to play certain champs, and to figure out if you want them. Sorry, this took forever to explain, but I was just curious as to why something like this doesn't exist.