Thoughts on the event
Personally I hate this event, getting rid of all but gen 3 has really made the game boring for me, my town is just filled with rosellia and gulpin, the new pokemon are either so rare that i haven't seen one in the 10+hours I've played so far, or are so common that I got them in 15 minutes, they got rid of all of the fun and challenging tier 3s, so there is no longer a challenge in the game, the only thing keeping me occupied is rayquaza but it won't be long before I am fed up of them, what have you done niantic. I can do a 3 man rayquaza but I am a long way off of a 2 man, so I won't be able to do that by the end of rayquaza which would be the last challenge left
Answers
I've found 4 Beldum so far which is likely 4 more than I would have found if gen 1 and 2 were competing for the spawns, so no complaints there. This is such a short event that there's no time to get bored.
I agree about the raid changes, they suck. I never got to solo C/SB and C/FB Alakazam with 6 different mons. There's a few one-mon solos that I can occupy myself with for a while but after that it's just going to be a long wait for the next rotation. I'll dream of getting Gardevoir to the tier 3 pool, that would be a fun solo for sure.
Next to the Valentine's Day event of 2017, this is probably the most lucrative event that we've been offered. Seeing very high amounts of non-nesting spawns like Trapinch, Anorith, and the like.
I've also seen a decent amount of Beldum and Bagon, try looking in Industrial biomes for them (look for where you normally find Machop)
I realize that the face of this event heavily depends on what weather your area happens to have during it, but you really can't go wrong with any of them:
Partly cloudy: Swablu (potential shiny), Aron, Lileep/Anorith (non-nesting), and Slakoth (non-nesting)
Cloudy: Ralts (non-nesting), Makahuita
Sunny: Starters, Lileep (non-nesting), Trapinch (non-nesting)
Rainy: Surskit, Lotad (Both non-nesting/weather dependent), Wailmer, Feebas (non-nesting)
Windy: Ralts, Bagon, Beldum (all non-nesting), Swablu (potential shiny)
Snowy: Beldum (non-nesting), Snorunt (potential shiny)
Foggy: Sableye (non-nesting), Shuppet/Duskull (all potential shiny)
If these mons seem like they're spawning more often, particularly those of whichever weather you're experiencing, don't get used to it. This is one of the shortest events we've had - and it should be due to the nature of it - but this is also a great opportunity to get huge amounts of rare non-nesting Pokemon like Ralts!
The best part about a lot of these species is that most of them are actually pretty good!