Reliability is probably about the same, but the Microsoft account signup process is a nightmare compared to the old Mojang system. There's like 4 different X-Box or Game like websites with slightly different usernames and they don't talk with one another and various features are scattered across all of them. Even flipping the switch that lets you join an online game is buried half a dozen menus deep in the bowels of the system and is labeled in a way that you'll never find it if you didn't Google for the instructions first. It's so unnecessarily complex and confusing.

The worst part is that some bot years ago signed up for the X-Box account using the same email I used for the Mojang account so converting the account first required me to take over the bot account with a password reset. But the bot set the account in up German and it's apparently impossible to switch the language settings for everything. I got most of it switched over (across four completely different configuration pages), but stuff like the emails are still sent in German. I'm pretty sure my account is going to be locked sometime in the future once they figure out that it was originally a bot account and there is no chance I'm going to be able to get my alpha Minecraft account back when that happens.

The Mojang accounts weren't great for security. No 2FA or anything (just security questions), and if you lost your account / it was stolen, you were pretty stuffed. The only way to recover it was to present the transaction ID of your purchase of the game to support, which most people don't have and you were never told to keep. I saw lots of people get permanently locked out of their accounts.

I guess it also doesn't make sense for them to maintain a parallel login system when the Microsoft one gets (presumably) millions of dollars of investment every year. Though Microsoft accounts are more complicated to use, with configuration being split across Microsoft, Xbox, and Mojang/Minecraft itself. And it seems they like locking people out for opaque reasons.

As a random example, if your Microsoft account is OAuthed to a GitHub login, and you log in through that, the popup browser just takes you back to a Microsoft account settings page instead of handing the OAuth flow back to Minecraft

just like google, it might randomly lock you out based on heuristics or ask you to add a phone number to proceed.