If you are going to do Enterprise APM, you need a full APM stack: logs, commands, synthetics, real user and byte code instrumentation. There is always an advantage in going with a single vendor vs. ‘best-of-breed’ and the consolidation is just a reflection of the industry maturation. Sure, it might look like the “Death Star” but it is still smaller the hundreds of apps present in an established enterprise – even if you limit your APM to tier-1 services.
Regards the “declining shares” of the big players, I think this has more to do with the decline in infrastructure management (IM) vs. growth of APM. You become proactive in your performance management by catching problems pre-production – rather than precise measurements of the crater you make in production.