Not every players gets a chance to acquire a top tier legendary Pokemon. Maybe you were unlucky and it ran away. Maybe you joined too late or you are a returning player who missed the boat. You could trade for it but that requires being on a good friendship level with another player. However, trades for legendaries can be really slow if you want to build a team of 6. The game currently limits it to one per day, regardless of friendship level. Then there’s the issue of the Pokemon you receive having mediocre to average IVs. Even if you do have legendaries, they can be expensive in terms of stardust and their candies are often in short supply.
When all that’s said and done , it’s better to consider other options which will help you do better in raids faster. You’ll very likely pick up better Pokemon with each Community Day you attend and as they are released through Raid battles or into the wild. For now, you’ll have to consider the cheaper, less effective but still viable options while you build your roster.
Below you’ll find a series of articles listing each and every alternative depending on the raid boss or gym defenders you seek to overcome. Each will judge how useful the substitutes are based on ease of getting candies, its movesets and stats along with how it stacks up against the competition.