I don't like HD wallets in general, I like the old approach better. Im not sure how exactly this HD wallet works, I just like the original format. As far as I know, there is no seed, so the wallet cannot be generated unless you own the wallet.dat file which is good, I wouldn't trust a wallet that can be generated with a single seed containing all of your private keys.
Clearly you don't understand how HD wallets work. Bitcoin Core does not use a seed phrase that you are probably thinking of. Seed phrases are not required for an HD wallet; you still have to own and hold the wallet.dat file. The only thing that changes is how the private keys are generated; everything else about how they are stored and the backup and security measures that you must take still exist with Bitcoin Core's HD wallets. It still uses a HD wallet and the private keys are still stored in the exact same format as before.
What are the pros and cons of the new HD enabled wallet.dat compared to the original format? I've had the same wallet.dat since Bitcoin-qt in 2013-ish and I never had any problems with it. But now with all the fork nonsense I will be forced to move my coins into another wallet, and when I tried to generate a new wallet in the new versions of Core it was HD-enabled.
With an HD wallet, you can restore any backup of your wallet.dat and still be able to access your Bitcoin whereas with non-HD wallets older backups may no longer be valid (they don't contain later private keys). However if your wallet.dat file is stolen, then all of your private keys for that wallet.dat file (including those that have not yet been generated used) are revealed. But you should be using a new wallet.dat file anyways if yours is ever stolen, regardless of HD or not.
To disable HD wallets, you must start Bitcoin Core with the
-usehd=0 option. However this option and the ability to create a non-HD wallet has been removed for Bitcoin Core 0.16.