No it is TERRIBLE for every class to be "equally good at taking turrets".
Let's ignore the obvious oversight of TANKS being equal at taking turrets, which would be idiotic and instead just focus on damage dealers. OK, so Mages & Assassins are supposed to be good at BURST, (ie. kill you in one shot) whereas ADCs are supposed to be good at DoT. This means in 0.1 second, a mage/assassin can potentially do 1000 dmg to a single target, but then needs 30 secs to do it again. OTOH, an ADC can do 1000 dmg in say 5 secs and keep doing that until someone stops them.
Here's why it is bad if the ADC and Burst take towers at equal rates. As an adc, I SHOULD lose to Burst in a 1v1. If the Burst can then take down a tower in about the same amount of time as me WHY WOULD YOU EVER PLAY ADC?!? The point of my sustained damage, is that you can't leave me alone to "free fire" on that tower because I'll tear it down, but I'm not safe just fighting you by myself. That's how these classes even out. ADCs were in a bad place with overpowered Crit because ADCs HAD lots of early Burst, but now the pendulum has swung in the opposite BAD direction.
Was it WRONG that ADCs could burst mages in 1 sec? YES. Is it EQUALLY wrong that mages can burn towers? Also YES.