Thornmail Ashe is the correct approach?
Sorry, but Riot still needs to teach at least the basics so people can go into their first games and not have dumpster-fire games. If the tutorials tell you to do something that will 100% cause you to lose the game, then they are terrible tutorials.
There is a WORLD of difference between telling the player what items to buy on what champions and just telling the player what items/stats even do. League's tutorial doesn't train people to find good information. It just gives bad information. A new player that goes through the tutorial then builds Thornmail Ashe in a real game and gets stomped isn't going to know which guides are good or bad. They won't know what they did wrong and won't know what to look for. This is why the vast majority of LoL players (keeping in mind the vast, vast majority of players are low Bronze and unranked) don't know how to build at all even after playing for years. Some people after playing for years still don't know proper last-hitting and lane management - because the guides they looked up were bad so they had no idea they were missing vital info.
Riot needs to either make proper tutorials on all important aspects of the game themselves or find the absolute best sources of player-generated tutorials and officially link to them in the client so everyone has access to good, correct info.