The tests i conducted showed that yes weight and possibly height are relevant to a pokémons statsfrom what i saw for two pokémon of the same cp the one with higher weight will have higher hpthis means that it is more important to hold on to heavier xl pokémon and place less emphasis on raising xs pokémon. From generation vi onward if a pokémon changes form any previously accumulated weight modifications due to autotomize are lost. Some players have found that lighter smaller pokémon are more powerful than larger heavier ones. Weight is stored with a granularity of 01 kg. If an effect halves a pokémons weight the result is rounded down to the next lower multiple of 01 but cannot drop below the minimum 01 kg. Some have found the exact opposite.
This all leads to one big question. Does a pokémons weight or height actually mean anything in the game. For example the likes of low kick body slam. When it comes to strength and battle skills we still have no concrete answers. For example hard hitting types of pokemon like rhyhorn should be xl in weight for greater damage and smallermedium pokemons that dont hit as hard should aim for xs or normal weight for a balance of speed and damage output. You have 1 stat that should always be xl which is height for maximum hp and 1 that depends on the type of pokemon.
As you can see from the graph here their findings showed that both the height and weight of pokemon had no effect on the hp of pokemon. There is another reason why size matters in pokemon lets go and thats all about the amount of damage theyll dish out when using specific moves.