TinyMCE is configurable. Right now we have it set to accept only strictly valid XHTML 1.0, which is the header used by HTML email content sent through Infusionsoft. What "common HTML tags" is it still stripping out? We can probably set it up to allow it.
They update with patches / new features quite regularly. For example, we reported a bug to them and they fixed it in 2 days.
There is also a vast array of plugins and customizations available for it that we have not yet begun to explore including in Infusionsoft.
I'm a huge fan of TinyMCE in case you couldn't tell.

Sorry for the derail!