Lhynn Consider a Level 1 match up. Wizard with 16 INT casting a L1 spell vs a non-proficient stat with +0 bonus. Effectively (8+2+1)=13 vs 1d20. The defender has a 40% chance to succeed. Round 2 65% chance. Round 3 >78% chance. Stated differently, a typical wizard using their best stat as a 40% of failure round 1 against a something baseline (no bonus, no proficiency). They can do that twice a day. Round 2, there is a 2/3 chance that spell will be shaken off. Unless the wizard has awesome initiative, there is a good chance an effect may never even get to be capitalized on. While a down the road maxed mage vs baseline might be 19 vs 1d20, characters have lots of ways to shake off or avoid effects. Even without items.
Changes to spell casting in 5E kind of took the worst from 2E, 3E, and 4E and mashed them up. It's not irredeemable, but there's so many tweaks to be done that a totally fixed system would be considered wholly different.