Having a T2 chip is not actually much more secure compared to let say Linux LUKS disk encryption. This is because T2 chip partly relies on obscurity for its security. Meaning we really do not know how things are being done inside the T2 chip. Who knows there is a backdoor or since it can't be audited by 3rd party then we can't really say that the system is to be trusted because in terms of security the first thing to take into consideration is TRUST and trust means transparency.
One argument of having a T2 chip is so that key management is not done by the OS or CPU which might be compromised already. But my take on that argument is that, if the OS or CPU is already compromise then the T2 chip can not protect your data because it will happily decrypt the data and serve it to the OS. I don't think it has the facility to detect if the OS is compromised. I don't think disk encryption was design to protect your data while the machine is on, i think its core design is protecting data at rest.
Another feature of T2 is it always encrypt your data in the SSD whether FileVault is On or Off. FileVault turing ON means merely requiring you to provide password before T2 chip starts decrypting the drive. This means that the master key for decrypting the drive is stored inside the T2 chip and is not protected by your own password. This means anyone who can gain access to the T2 chip will be able to decrypt the drive. I think thats where the obscurity part is involve. Since no one knows except Apple on how T2 chip is managing the keys inside then we are just hoping no one will be able to hack or defeat the whole system. But of course Apple technicians can always access the T2 chip and probably can decrypt your drive for you. And thats a problem since you really don't have total control on the security of your data. It is different from let say Linux LUKS disk encryption in which it will create a master key for encryption/decryption and encrypt this master key using your password or passphrase. This way no one will be able to decrypt your data without your password. Of course they can always torture or intimidate you so that you will give them your password
So to the question, do you really need to lock the drive to the T2 chip to provide better security. I don't think so.
I wish they could have just implemented it in a way that every time you plug-in a different SSD the T2 chip will format the drive and generate a key for that drive and start encryption/decryption on the fly. This way you can swap your drive without the need to visit Apple which hold the key to your SSD. Sadly you do not hod the key to your data
And also, if the T2 chip dies then there is no way to recover your data without recovering first the key. But fortunately T2 chip is robust enough that they don't just die on their own.