The big difference with Lemmy is that it's not really a service, it's a open protocol and standard, like email, or http. The service itself is provided by distributed instances that adhere to the protocol. Like those protocols, no one company has been able to get a monopoly on it. Some have taken over a lot of it, like Google with Gmail, or cloudflare, but if you don't want to work with them there are a ton of other options you can go with, and you will not be locked out of the system if you do.
Reddit was a centralized closed source system so if you don't have a Reddit account then you are locked out of the system completely.
Lemmy is decentralized so no one instance has or can gain a monopoly. If you want to break ties with one instance you can just switch to another one and still participate with it and the rest of the fediverse.
Not only does that give you choice in a worst case scenario, it also keeps all the instances on their toes because they don't have dictatorial control over their users.
Spez's fatal miscalculation was that he thought he had user lock in, but unlike other social networks where it's your only option to keep in contact with your real life friends, or it's the only platform your favorite creator posts on, they had neither. Almost all accounts were not connected to your real life and posts were mostly links to other platforms. Very few creators had Reddit as their sole posting platform. The interactions were ephemeral and superficial. Dropping Reddit was the easiest service I ever had to drop.
Let this be a lesson to all devs out there. Never do work for corporations for free. Only contribute to FOSS. Devs are the backbone of the internet and before the fediverse there was no outlet for them to work on actually distributed platforms as opposed to libraries and utilities. If you want to do work on a social platform do it on the fediverse where you don't have some heartless corporation exploiting your free work and not appreciating anything you do.
Reddit should have been paying their own devs to do this themselves. This is literally millions of dollars worth of dev work.