The players talking about high ground being so easy to get in a battle, are assuming you know that there is a battle coming up and can spread your characters around and prepare for the battle. Once EA is over and the game is released, you won't know when all the battles are going to happen and where. So your party will be walking along, and boom, you're in a fight. You're clustered together and now need to move, prepare and attack on the fly. Just re-load, you say? That's where immersion is broken. By the time you can get your mage to high ground, they have probably already been killed by the enemies. Fairy Fire, Guiding Bolt, etc are extremely useful spells in PnP due to the fact they they do give you advantage on subsequent attacks without the need for high ground.

My point being, if you are playing straight through without reloading, the high ground mechanic is going to practically cripple you as your party is just walking along on your adventure. I believe this is why it's not implemented in PnP. If you are getting ambushed by monsters on high ground, it will be a TPK due to the fact that the enemy has advantage on EVERY attack made against your party, and you would have disadvantage on EVERY attack against them until you could get party members up there to push them off or something similar. In PnP, they would get advantage on the surprise round, but then normal attacks after that, and you would have normal attacks every round against them. This seems more balanced to me.

To HAVE to take Misty Step, and similar mobile spells just to make it through the game seems kind of silly to me. To HAVE to take any spell because it's crucial, otherwise you will have a hell of a time seems ridiculous, but again, that's just me.