Adizero Boston 9

The Evo could be a dedicated speed shoe but that's not really it's use case. It's a daily that can do speed work vs. more dedicated speed shoes like the Saucony Endorphin Speed, Asics Magic Speed, Puma Deviate Nitro, Adidas Boston, etc. Dedicated speed shoes usually have a plate or rods. Daily trainers that can handle tempo/speed work like the Evo, Saucony Azura, Puma Velocity Nitro, and Asics Noosa Tri don't have plates. At the end of the day, categories aren't hard and fast and you can use a shoe how you want. How the shoe ultimately works for you is most important.

It's hard to say since you didn't like the Boston 😅. It's the only one in that category I've tried and liked. Deviate Nitro were too narrow for me even with sizing up a half size. Haven't used the other two.  I mostly do my speed work in carbon racers as I've collected a number of them figuring out what I like and don't like so I just rotate through them.

I mean...no. The Megablast is a do everything shoe that can be raced in at marathon distance. The Evo SL is a daily trainer that can do speed work.  There's overlap but calling the Evo a worse Megablast is disingenuous, they're different categories of shoes and priced accordingly. You can often find the Evo SL for less than half the price of the Megablast.  The Megablast also has almost 9mm more stack in the heel based on actual measurements and 7mm in the forefoot (RunRepeat). They're just not really that comparable.

In a general rotation? They don't serve the same purpose. Again there's overlap but that's not the same thing.  In OPs they could potentially serve the same purpose but I wouldn't recommend either as the dedicated speed shoe if that's really what OP is after.  Again it's not a worse version of the same shoe regardless of why/how you use them and your opinion about subjective criteria related to them 🤷🏻‍♂️ .