The challenge that nations such as France, NZ and Canada face when deciding to upgrade legacy types is that they become increasingly expensive to operate. This is particularly so as the upgrades turn each type into a tiny, unique fleet each requiring bespoke logistics support. Inevitably, further upgrades will be required as systems simply become unavailable, or for the aircraft to remain legally able to fly iaw Global Air Traffic Management requirements. In contrast, modern types often enjoy access to commercial, globally available spares networks. This is a major benefit of the RAF Sentinel fleet operating in the Middle East and Africa which has exploited Bombardier's business jet logistics support for routine airframe and flight avionics.
In short, a more complex, modern type may not necessarily be more expensive to operate, particularly in the long run. Nor are they necessarily more difficult to operate from austere locations although I accept that weight and runway requirements are a factor. That's where cheap and cheerful types such as King Air 350 and PC-12 variants (or RPAS) can come into play. Granted that the CN-295/ATR-72 MPA also enjoys similar benefits. However, such types are enormously compromised in terms of 'blue water' capability. And with modern ASW, any compromise - whatsoever - effectively means no capability.
Sadly, there are no shortcuts to staying in the ASW game.
Regards,
MM