Dialga: Raised to A+
Dialga is a hugely versatile pokemon and it is one of the most underestimated pokemons, and it is better than it's current ranking suggests: it deserves a higher rank, A+ if not S.
It has an excellent typing: Steel/Dragon gives it resistances to many prominent offensive types such as electric, water, flying, psychic, and it is neutral to dragon, ice, fairy. even though it has lost its resistance to ghost types and dark types, it still has an excellent defensive typing, and the stats to back it. 100/120/100 are solid defensive stats, especially being backed by its typing. It might be weak to ground and fighting, but they are becoming rare. Fewer people are using groudon because of the drought nerf, kyogre factor and xerneas. Fighting types like blaziken and mewtwo-x can be checked by dialga in other manners. Offensively also its typing gives it STAB to dragon type moves which are very important considering ubers are riddled with dragon types, and the steel type, which can help defeat fairy types like sylveon, xerneas and arceus-fairy. In addition it has base 120 attack and base 150 special attack, which gives it the necessary raw power to defeat these pokemons.
It has an excellent movepool even by uber standards. It can learn support moves such as thunder wave, stealth rock, roar, toxic, which allow it to proficiently support its team by providing status, hazards and phazing support. It has an arsenal of attacking moves, with special attacks like dragon pulse, draco meteor, aura sphere, flash cannon, earth power, ice beam, thunder, fire blast, whereas it also learns physical moves such as dragon claw, iron head, earthquake, brick break, shadow claw, stone edge, dragon tail, allowing it to take the physical route too. It also learns moves like bulk up and can use it in conjunction with rest and sleep talk.
The amount of sets Dialga can run is innumerable. It can run a lead and support set with SR and Twave, it can phaze with roar or dragon tail, it can run a specs set to break walls with draco meteor and thunder, it can be a late game sweeper with a scarf set, it can go mixed, it can run a restalk bulk up set and slowly kill the opponent, and it can make use of a huge number of newly introduced items like assault vest and weakness policy.
Dialga is also very good at countering prominent threats in the uber tier. it can check xerneas with its steel type stab and an assault vest, it can counter kyogre as it resists its stab and can hit back with a thunder. it can beat mewtwo by spamming draco meteor and crippling it with a thunder wave. It serves as a good mega gengar counter because it can survive its attacks with its bulk and OHKO it with its own attacks. It resists extreme killer arceus' extremepeed and can spam draco meteor or aura sphere on it. It can break walls like lugia and giratina down with a thunder and dragon type STAB moves respectively, and defeat yveltal with ice beam or thunder. Also, it is neutral to dragon type moves, so it is capable of defeating a huge number of dragon types which includes rayquaza, palkia, giratina, reshiram, zekrom, lati@s, etc.
I have always been a huge fan of Dialga and I believe it is without a doubt the best dragon type pokemon and I hope other people realize why too. TO conclude, it has a great defensive typing, it has incredible versatility, capable of running support sets, defensive sets, special attacking sets, mixed sets, and it has very good stats, with defenses of 100/120/100 and base 150 special attack. It has a huge movepool, which also gives it so many options and it is excellent at checking dragon types and flying types of the uber tier in addition to newer threats such as xerneas. It requires little to no support because of its excellent defensive typing, vast movepool and stats. I hope the tiering council moves Dialga to a higher rank, because it is just that good.