Of course, Veeam has fewer problems with VMware, but VMware has been supported since 2008 and they have been able to optimize the product.
The Proxmox integration was developed within a few months and is of course not yet as mature on the Veeam side.
I already know a few upcoming features, but it's all still in the development stage. In a few years, the Proxmox integration will probably be as mature as VMware.
I can't support the idea that the problems are due to Proxmox. There are mature products like the PBS, which run great, only the veeam integration works a little differently.
If you want to continue spending a lot of money on Broadcom for your 15 hosts and a lot of money on Veeam for the 3500 VMs, feel free.