... Why does merged mining suck? ...
You answered that yourself:
...Just a bit odd looking at those low numbers and seeing 5 longpoll requests to every accepted share.
A NMC block is much easier to find than a BTC block. Each time a NMC block is found, your work is being interrupted by a LP message. The current work and queue needs to be dumped and new work needs to be fetched. If your miner is slow, you might be interrupted relatively often.