Pokémon X and Pokémon Y

No. Because they brought some significant changes to pokemon, when Heart Gold/Soul silver really didn't change anything up.

Sinnoh games -
Most importantly, separated pokemon moves into special./physical on a move by move basis, rather than by type as in all previous games.
106 new pokemon.
Online battling (And trading I guess, but I never used that).
Being able to double battle team up with a npc (I think this was new in D/P anyway, correct me if it was in a gba game).
And then platinum made large improvements to the battle frontier (Which was then copy pasted into HG/SS)


HG/SS added... you getting a pokemon to follow you? Yeah. I didn't care at all about that. And I can't think of anything else that HG/SS did to change the way pokemon was played, or distinguish itself from the other games. Oh, it had two fairly barren regions instead of one meaty one, I guess, that's "different".
Plus they still didn't fix that HG/SSs wild pokemon STILL ended at about level 40~50. Which was fucking retarded when you're supposed to somehow get from 60ish when you beat the last gym leader in (The most barebones region ever, remake kanto) to 80 to battle red.

I didn't realize that the mechanics that the respective games added were the only basis for the comparison. The mechanics were great, but the games themselves felt not only bland, but slow and clunky. A very large number of the Pokemon added were unmemorable or had very goofy designs - especially the legendary Pokemon. Lake Guardians, for instance. There's also the issue of the distribution of Pokemon (both wilds and trainer battles), such as the very noticeable lack of fire types (even the fire-type E4 member had mostly non-fires on his team), or the abundance of Shellos/Geodude/Ponyta. Shellos was the new Tentacool. The soundtrack was mediocre as well - very few tunes managed to stand out. Perhaps Mt. Coronet and Cynthia's theme and that's it. Platinum improved on the distribution issue, but not by much.

HG/SS, being a remake, wasn't really the place for large-scale innovation - but that doesn't necessarily make it bad. It's a very good example of a remake done right. Vastly improved UI, Voltorb Flip is a cool minigame, significant rebalancing (no more elemental punches out of Goldenrod, Kanto is no longer made of paper, Whitney's Miltank isn't a fat ball of death), better music in most cases (RIP Champion battle theme), lame areas were improved upon (Whirl Islands, Mt. Silver, most gyms, and Ice Path/Dragon's Den to an extent), increased use of the touch screen, as well as gym leader refights - a very easy way to level past 60 before fighting round two of the E4, or Red.

Basically the Sinnoh games were bad games with awesome changes to the Pokemon "formula" and HGSS was kind of the exact opposite. If you judge the games almost entirely based on what they changed about the formula (instead of the games themselves) then it's natural that Sinnoh will look like diamonds compared to HGSS.