These days it doesn't actually make a huge difference. Or rather, it depends very strongly on your backup plan, disaster recovery plan, your RPO and RTO and the scenarios you expect to want to recover from.
In any modern environment; you're likely to also have some sort of SAN. Your backup solution should interact with the SAN, but not the rest of the network; this allows you to back up data without exposing your backup solution to risks associated with the hosts you're backing up (this is a generalisation).
The decision between disk and tape should come down to your environment and your requirements. If you need to store your data for a long time: tape, properly handled can last decades, so as long as you test their integrity every ~10 years, you should be pretty safe. It is cheaper per GB (in the order of something like 90%), and the principles behind storage and retrieval are well understood. It is however, very, very slow compared to disks.
Disk can potentially be always available, it is a lot faster and lends itself to replication via WAN/etc. - but you generally have to leave them on and running to verify their integrity, and buying more disks can be a limiting factor if you're keeping your data for a good amount of time (how many fit in your array?).
In most environments, you have a combination of disk and tape; certainly for environments with any sort of compliance overhead. Disk backups deal with replication and hot site DR, tape deals with historic backups and long term storage.
To answer the question:
Is physical tape backup better than disk to ensure integrity?
It depends on how long you're storing, your backup cycle, and what you're backing up for (will you need the data in a hurry?).
So what do you think about tape vs disc? Particulary in financial institutions.
I think any serious environment will likely have both. Particularly financial institutions that require high availability and minimum downtime - if their server room floods, you'd expect them to be up at Site B very quickly (so, from disk), and if they need to dig up accounts from 30 years ago, I'd expect them to be able to by going to their tape library.