This icky tradeoff is why new (as in pre-IPO in some cases) vendors can still get a fair test in existing networks. Eng&Ops type people have told me more than once that they thought $NEW_ROUTER_VENDOR could be a good investment simply because nearly 100% of their engineering resources would be dedicated to making their small number of customers happy, and being a larger customer amongst a small set increased this advantage even more.
.. which is certainly true until small $NEW_ROUTER_VENDOR IPO'ed or otherwise grew into not-so-small $NEW_ROUTER_VENDOR, as we have all witnessed on numerous occasions. At which point, they're all the same again. You only gain an advantage for a limited amount of time. There are costs attributed to this as well which need to be realized.
The big challenge at an established router company is in management of the competing priorities more than in management of, or doing of, engineering.
And there also is a business reality. If you get almost everything right, most people are happy with that. Few people demand, need, and can afford to pay for perfection. In fact, one could argue that it is poor design to rely on anything to operate perfectly 100% of the time. Now, if lack of infrastructure realiability can harm human life you may feel differently, but that isn't the case for most of us at the present time. We can sit here all day long and argue back and forth for strategies from multiple vendor based networks to why single source offers advantages to why bla bla is cool. The bottom line is that there is no free lunch here. If you want perfection, you will pay for perfection either in house or for your vendor or lost revenue or all of the above. And sometimes business cases cannot support perfection. The trade-off that has to be made here is how much "slack" you can get away with while still making your customers happy and at the same time supporting your business case. Anything else has no long term viability. From an engineering perspective this view certainly stinks, but when you take into account business realities engineering's perspectives may be an illusion. It's the old wisdom of 'pick any two: cheap, fast, reliable'. Faults will happen. And nothing matters as much as how your prepare for when they do. Cheers, Chris