That situation you detail is no different to other aircraft that have new generations available.
The A330neo has its advantages and disadvantages, but if airlines want the capability and efficiency, along with the likelihood of lower maintenance costs, they will look at newer planes. If they take into consideration that older aircraft may not be as efficient on the missions they fly but have lower costs of purchase/lease, then that opens up other avenues.
The situation I detail now is certainly different for airlines now than for airlines say, 10 years ago making the same fleet decisions.
In say, 2010, if an airline wanted a proven middle-of-the-road aircraft, the only practical choice was the A330, there was no equivalent feedstock of older A330s as competition because A330 deliveries only ramped up by like 2005 (meaning less returns from leases/less leasing activity to begin with) and the early A330s were pre-hgw and significantly compromised in capability. Hence we saw the order and delivery binge for A330s during that time.
Now in 2019/20, if an airline wants a proven middle-of-the-road aircraft, they can choose between new 787s, A350s, A330neos, and A321LRs depending on what routes they want to fly. There is also a ready feedstock of capable older A330s (many delivered from 2010-2015) which will be returning from leases in the next 1-3 years. That's a ton of competition which the original A330 never had to deal with.
10 years ago, their were heaps of used 767 and A300/310 on the market, having been replaced by increasing numbers of A330. There were huge orders of 787 waiting to be delivered. Than the he days of A330 deliveries arrived. Most of those A330 are young, no reason to believe that they will flood the used market in the very near future. Most used A330, apart from some really old ones, do find new employment fast. Increasing numbers will be converted to freighters, when prices for feed stock drop.
In regards to a slowdown or insufficient order numbers, all orders for all frames are rather slow. What wide body frame has the most net orders so far this year? Actually the A330-900.
Let's address your arguments one by one:
- "10 years ago, their were heaps of used 767 and A300/310 on the market", Many of which were 15+ years old and EOL with diminishing OEM/Maintenance support, this is simply not the case here
- "There were huge orders of 787 waiting to be delivered." 787s were far from proven in the early 2010s.
- "Most of those A330 are young, no reason to believe that they will flood the used market in the very near future." Many of those A330s were signed on 8-12Y leases with lessors who are sweating right now to place them with other airlines, and from what I am hearing, they're having a damn tough time doing so because the first-lease airlines want new widebodies, and the usual airlines wanting used planes are re-thinking adding more widebodies and favoring narrowbodies instead.
- "Increasing numbers will be converted to freighters, when prices for feed stock drop." this will necessitate big write-downs on the owners at their current book values, and therefore will take a long, long time before that pans out.
Those 2010-2015 delivered A330s are mostly 233-235t versions, which make them insufficient for many airlines even they want to buy or lease from second hand market. Those 330s are good for under 4000nm cargo heavy missions but if you want to fly further with heavy payload you need something else. Finnair is good example of that. A330neo is much more capable than its precense.
Finnair is a good example of an airline that may have been on the market for A330neos but has seemingly chose the A350 instead, and besides, "under 4000nm cargo heavy missions" describes the vast majority of current A330 routes right now.