Well if I understood correctly the features are "blocked" to mitigate the current ddos. The thing is, even under ddos, Mangadex still get faster loads time on good quality pic than Mangarock have on low res.
MangaDex is still young and kinda prioritized the feature it was meant for, the reading ones, the community ones, while MangaRock seems to get all eye-candy on poor bandswitch making the functionality that should be the main one (the reading part) kinda a hassle. It's like commercial jam vs home-made one, one get good packaging, low fruits and bad sugar, the other get the taste! It can on an other hand create envy, and keep a reader on the site.
I still use first version of the UI on mangadex as I prefer the listing way, I find it more smoothing for the eyes than the dual collons and so I don't like the heavy MangaRock UI.
The MangaRock suggestion thingy is interesting if you read all that pass across your screen, if you are more of a "seeker" the MangaDex tags are better. Also, those tags can clearly be used to make the same "you may also like" thingy in the future, I dare say with a more real audit. Last but not least the mangadex devs, are way closer to the community/user and integrate requested features while dealing with technical difficulties, while if you just look on the beta corner of both the MangaRock site and app, the number of support for a request - like adding MangaDex as a source XD - and the answers...
Well, but some users don't really care about that, they just access to content, so atm the 504s and the "need to log for using the search function" can be a big let down for them.