Thats totally theoretic that they'll slow down progression, because many games without microtransactions are aimed currently for unlimited progression.
This game does have microtransactions. And like all games that have them, there is all the incentive in the world to alter progression so it favors using them.
Because there are always people who exploit, who play better or play two-three times more, so why shouldnt be there players who pay? If You want to be so fair to other players, You should also be push that games should have play hours to do not get unfair advantage other working people etc.
Exploiting game mechanics is IMHO irrelevant to the discussion. There are (presumably) systems in place to prevent exploits, and deal with users who abuse them. If there are not, the software is fundamentally flawed as a competitive multiplayer experience out of the gate, and any talk about fairness or options for progression becomes meaningless.
You say that we should be able to pay, so that those with more time or ability don't have an "unfair" advantage. What is unfair, exactly, about putting in time and progression that others do not? I could easily say it's unfair (or terrible design) to equate someone willing to put hundreds of hours into a title, with someone who just started but is willing to throw vast amounts of real money in instead. An unfairness still exists, but now it's not based on skill or time invested, but on disposable income. So the idea of introducing "fairness" by adding real money transactions is not a solution.
There was never 'same level playing field'. There are always players that exploit, play more or better, thats a fact.
Check Path of Exile's, which is of one the most consumer friendly games on the planet, races/leagues for example and try to compete with players like Kripparrian or Willy.
That is in fact the result of the level playing field. Someone willing and able to devote more time and energy to something
should be rewarded with progression/loot/what-have-you, wouldn't you agree? Without real money transactions, everyone is on the same track, with the same obstacles, and the same commitment needed to overcome them--you can be assured anyone with an advantage earned it through actually playing the game.
Mass effect 3 did it pretty damn well. Also let them make significant additions for free.
Fair enough, they certainly can be done well--like all content delivery options, it's all in the execution.
I'll acknowledge microtransactions are not inherently bad, they just tempt publishers in bad directions (e.g. Dead Space 3).