WotC has already addressed this issue.
The middle ground is : supernatural / spell like abilities are contained in the spell block, genuine spell casters use PC caster rules.
In the very particular case where you DM an adventure module published by WotC AND you feel overwhelmed by playing a spell caster AND you don't want to spend any time to either read / summarize / change the spells AND you're not ready to wing it up, I guess you are in mild trouble 1 encounter out of 10.
I sympathize, though, as I find the Keywordic editions (4e, but also 3e) much harder to DM than those less jargony. But clearly, 5e seems to be already more user friendly on this front.
Rather than copypasta of summaries that should be written on the DM screen, I hope published adventures would provide tactical guidelines for the complex monsters. Having a clear statements of the effects intended by the designers is much more enlightening for the DM, and also for the players as they are using the same toys (and I find a dual wielding rogue more daunting to play - deciding between Cunning Action or an off hand attack, getting hiding and SA opportunities, etc. - than a basic Wizard).