I found the manga telling of the Dark Kingdom arc to be just all right in all honesty, and I didn't like how the guardian senshi weren't directly involved in the denouement. Which is why I'll always prefer the classic anime's version of that arc over Crystal.
However, R vs SMCS2... well, SMC wins only because I guess I never really cared about R except for the Makaiju filler oddly enough, episodes 68 and 69 (Luna's speech to Mamoru was great), and the Ayakashi Sisters. Plus Pluto was better developed in SMC and makes up for thin role in the old series.
As for the ongoing character development arguments... well, the old anime used episodic and slice-of-life storytelling to flesh out characters a lot of the time. Most of the anime released during that time that I watched did that, too. In Crystal, the character development is there, just more sparse. Unless it's Usagi, Chibiusa, Pluto, or Mamoru. Even Luna was better developed than Rei, Ami, and Minako for the first season. Makoto had her sad stories in S1&S2 so she was the best developed of the four guardians. Other than Makoto's subplot in the most recent SMC episode, I guess I'm failing to see significant character development for the other three girls. Ami threw a pencil at a camera and dove into a pool, but that just seemed more action oriented storytelling than anything contributing to her character's growth. They didn't even return to her subplot in the end of the story as it was all about Haruka and Michiru again. Anyway. Rei and co. definitely have personalities in SMC. I just struggle to say what those are at times because of the tightness to the story and the lack of time to give them the attention they truly deserve. Or I'm just piecing their personalities together based on the old anime and anything loss in translation from manga to television. If the show is going to be so neck-and-neck with the manga pacing wise, then yeah, it's to be expected. If each arc was longer, then I imagine the supporting characters would be more developed. I think the overall Infinity story (which I personally find to be more interesting than the DK and BM arcs) and better action/animation quality in S3 is all helping us gloss over this flaw.