It doesn't say anywhere that the landlord is required to supply you with a separate freezer- yes, a freezer box in a fridge is damn small, but thats the norm.
The landlord is offering to get you a new freezer with a 50% contribution from you- and to keep the freezer when you leave. Seems reasonable to me. If you want a separate freezer- and you want to bring it with you- buy it yourself. They start at about 140 and go all the way up- Powercity and DID will even deliver them for you (at a cost of about 20 Euro).
Its not normal for a rented house or apartment to have a big separate freezer in this day and age- for better or for worse.
Personally- I'd go with the landlord's offer- unless you have a particular wish to hump a freezer around with you in future?
Ps- when you do get a new freezer- read the instructions about leaving it running for 24-48 hours before using it- this cycles the refrigerant in it etc.......