Validation offers little business value. My reply was perhaps a bit old-fashioned. Why eat your plate, when you can only eat desserts? But validation is a prerequisite for accessibility. Accessibility may or may not add business value -- like an architect that designs houses for people between 190 cm and 165cm might not ever face a problem.
I think Pingdom is not about page speed, but ping speed. Things like javascript resources won't be downloaded in parallel right now, no matter the Pingdom score: combining your 7 jQuery plug-ins will increase page speed.
You really need a front-ender for the exciting stuff, I agree. A statistician with front-end experience would be even better.
I understand that in iterating fast like you are, you might leave some crumbs, to move on to bigger and better things. But also in practice, as a good front-end developer, part of a good team, it is possible to validate and speed-optimize even the largest of sites.
And the multi-functionality you rightfully demand from a front-ender, you can extend to every scrum team member. That means if the front-ender hands in a valid template, back-end devs should take care (know just enough) to not invalidate it.