The problem about Ronaldo isn't Modric. It never was, it isn't and it will never be.
The problem about Ronaldo isn't his level in past years. He was extraordinary, he always was, and that was never in doubt.
The problem about Ronaldo is that he wanted a 4 year contract, from 33 years old until 37 years old getting very huge wages in all of them, and forcing Florentino to have one more motive to renounce to some other interesting players in his same position (Neymar, Hazard, Vinicius development etc). Thus, conditioning the sports model of the next 5 years.
That's the whole thing, not what might happen in September and October this year, or even the whole season.
I always say the same, every club dreams of signing players just before they start to shine, and selling them just before they start to decline. Is Ronaldo starting to decline just right now? No, quite probably not, but the alternatives were 4 years or nothing, and that's what the whole thing should be about.