Playing Variants Makes You Weaker

If you're interested in how variants affect your standard game, look for posts from top variants players here like @RoyalManiac and @TheUnknownGuyReborn . They know this better than everyone as they have played and studied for years, so if you really want a true, honest, and accurate answer, please read those responses in particular.

Being a fan of variants myself, I would also like to state my opinion on this topic. I would go as far as to say that variants that strongly differ from standard chess like Horde and RK do not affect a player's chess skills at all because it is easy to distinguish these variants from standard chess. A problem that I have come across when playing variants like Atomic or Three-Check is that standard games will be affected by forgetting that capturing pieces do not disappear or by starting really unsound attacks. That problem vanishes after a couple of days of not playing variants though.
An obvious effect that has been mentioned to a sufficient extent is that studying and playing variants takes time during which one could study standard chess. On the other hand, studying variants improves calculation (amongst other skills like studying openings) in standard chess, too. That is my take on the issue. But well, if you have serious aims at getting better at chess, you should probably not play variants. If you don't, just do what you like :)

#1 Horde has no bearing or affect on your regular ratings because it is just pawn pushing.

Playing anything makes me weaker.

Personally, playing a lot of variants will make me slightly weaker in standard until I go back to standard.

It's the opposite for me. Playing so many smothered mates or ways to win the queen with check in crazyhouse has helped me recognize the same pattern or tactic in standard games faster than before.

... at least not better.

Boby

Playing atomic helped my standard western chess (and xiangqi, and shogi) improve. The improvement was maybe about 200 points passively.

I would say that going into a variant expecting to get better at western chess is unrealistic, though. The main benefit of atomic I found was that it taught me about the flow of the game, and the training methods to improve (if desired).

A game of atomic plays out very much like regular chess: survive the opening, play a good middlegame, win a technical endgame. Material is important (a single pawn is a winning edge much of the time), and piece activity can compensate a lack of material, just as in western chess.

To improve at atomic (or any variant really), one needs to study: identify weaknesses (endgame technique? calculation speed? strategic grasp? opening lines?), then deal with the weaknesses by focused study. The details depend on the variant, but the general principles are the same across different chesses.

That said, I feel like in order for variants to help, you need to actively put effort into it. Study consciously and seriously. You won't learn much more about regular western chess if you can't grasp "how to think about the game".

Atomic taught me what is was like to be a strong player (although I was never at the very top), and in hindsight, how to get there (a lesson applicable to any other type of chess). Players like RoyalManiac and TheUnknownGuyReborn are comparatively even stronger, being top players in their variants, and correspondingly may have felt an even bigger benefit to their "weaker" variant of regular western chess.

Nor will players already strong at western chess learn much more from western variants; maybe from a different chess, like xiangqi or shogi, since it will open your eyes to different ways of coordinating pieces and evaluating a position.