While I am all for bashing D:I's predatory MTX setup, don't jump to conclusions based on one post.
The game has plenty free progression - you still have paragon levels just like in D3 and drops you get depend on your paragon level + difficulty you run content in. And there is A LOT of content types.
The gems issue is big, but it's not AS big as people make it out to be. It is true that a character that literally WHALES the shit out the game will be about 2x powerful (as long as they keep up paragon level - important point), but the base power actually comes from gear you grind out like in every game.
Gem resonance (which is what gems give besides base stuff) is a multiplier on top of gear you found - for example my multiplier is at around 30% now, while F2P player would probably have like 5-10% from gems they do get (you can craft them and such too). In my case I tossed about 100 bucks in game. Resonance cap is 400%, but nobody can get it because there are no gems to support it yet. One of the top whales has like ~250% resonance and the guy spent few hundred thousands.
My take is this: if they'd remove all this gem resonance and P2W gem upgrades from the game - it would be down right better Diablo 3 right there, as far as game itself is concerned. Simply because there is so much different stuff to do there in-between PvP, Raids and Shadow/Immortal game mode, that on top everything D3 got now like bounties, dungeons and rifts.
Quite frankly, I am almost shocked they did not introduce D:I game modes to Diablo 3, that'd be nothing short of expansion worthy there and would make it a much better game.