I do a lot of work in Enterprise CMS land and Open Source land and you've essentially described my experiences working with ALL Enterprise CMS's I've used since the early 00's. I'm pretty convinced that within about 18 months Open Source CMS's will have negated any residual technical benefits that Enterprise platforms offer.
At this point the only competitive advantage Enterprise CMS vendors will have is their reputation and the "nobody ever got fired for buying IBM" attitude and commercial support.
With many other businesses sprouting up to provide commercial support for open source platforms I can see many Enterprise vendors having to pull up their socks and shaking up how they sell and manage their platforms in the very near future.
You would think people focused on knowing just one product would know something about it.
This is especially true of Microsoft who I've had the pleasure of dealing with their highest level of Gold Partner support with respect to an IE9 bug that broke ClickOnce entirely.
Basically: absolutely fucking useless, blame the client, wriggle out of having to do anything.
That was until they met me. 35 phone calls (I shit you not), 3 heated arguments, spread bad press all over stackoverflow and MS connect, blog whinge and finally a half arsed registry fix that we had to deploy across 2000 disparate clients!
6 fucking months it took and we're a MS Gold Partner. It cost us more than our subscription cost in bad rep, time and support costs.
1) Realistic scaling. Just about every piece of enterprise grade software I've seen falls off a cliff when it hits a certain load point. This is ALWAYS enough to sell it to you. When it goes wrong...
2) When it goes wrong, it's a nightmare of maintenance contracts, verification, finger pointing and telephone calls that last hours.
3) It rarely works as advertised. I mean literally 1% works as advertised.
4) Trials and realistic evaluations without crazy constraints are not usually possible (this is changing slowly).
5) Installation is a breeze but when it comes to backup/restore and upgrade, it's a pain in the butt.
Time is money. The difference between "enterprise level software" and "OSS" platforms are the following:
* OSS time is spent up front.
* Enterprise time is spent later on and costs more up front.
I'd rather have one Ninja on the team and lose the enterprise software. Ninjas scale better as well.