Yeah you can argue that medallions made the game more skilled but traits and gems definitely did the opposite, and this isn't an subjective opinion.

Before 2.0, a ability would e.g. have 8sec cd and deal 14 dmg. A pro player could theoretically calculate/count down the cooldowns for every ability of every player in the match, and could calculate the dmg of his own abilities or the abilities of his opponents, and he could base his decisions around that.

After 2.0 the same ability had 8sec cd and dealt 140 dmg. Now with traits and gems, this ability might have 7.6sec cd and deals 144 dmg. But it could have 7.8sec cd and deal 148 dmg as well, and so on. There's no way to know.

And it gets even dumber. Before 2.0, a pro player could theoretically anticipate the exact movement speed of his moving opponent to hit an ability at max range, or he could count down the duration of the cc to hit Shadowbolt for example at the last split second.

After 2.0 movement speed can be changed, cc duration can be changed, energy gain can be changed.