I disagree with this tip for one main reason, there is so many things to learn when you start a game of Dota that just knowing what your own hero does, the items that you may or may not build depending on lane, and enemy team comp just to start. This doesn't even begin to touch the necessity of map awareness, having a tp, knowing how the runes work, how the jungle spawns, stacking, creep pulling, denial. I find that if you get a set of heroes you really enjoy that you ultimately will learn how heroes you don't play kill you and because you're familiar with this small set of heroes you begin to formulate specific rules for both specific matchups and general conceptual ones. I.E. When you lane against any lane with a double and or set up stun combination what do you do to avoid being killed? What level is your hero more powerful or less powerful than your lane opponents? Some lanes have incredible level 1 spells, Venomancer + Juggernaut is one such lane, and very few lanes stack up to the pure kill potential at level 1 that that combination of heroes has. Other lanes reach their kill power at 2, or 3 or 6 (ultimates). By playing one hero or a small set you begin to learn how you fail. There are many heroes that I have less than 5 games played on even though I have played thousands, and those heroes don't surprise me when I play them. I learned their toolkit by both killing them and being killed by them, but not by playing them. Conceptual questions about how precisely certain skills work can be learned by an in-depth look at both tool-tip examples and a quick Google search if necessary.
I believe one of the most difficult aspects of Dota, one that league specifically does not prepare you for, is the item shop(s) all 6 on the map, the courier and its importance, and then finally, the big one is the item choices themselves. One thing that never happens in league is gathering an inventory of items that have active use extremely powerful skills (each clicky is another skill to manage, potentially up to 5 items in your inventory could have active uses. There are very specific counter items or momentum items.
This is why I would also suggest lich as the best starter hero in the game, he has a simple nuke, and a skill shot nuke (to maximize its potential), a creep deny mana mechanic. You build Tranquil boots (heal) and a mek and you can now practice using items from your inventory without the stress of 4 active usable skills and he is more forgiving in lane when harassed because with just the tranquil boots you can regen all your health and mana without pond trips.
TLDR; Learning heroes you don't play is very possible and my opinion more optimal on a hero you play well. Skills you don't understand, look them up post game, or take a moment to check out the learn tab in the interface while you're respawning.
