Am I being undervalued as a co-founder at 19%?

I am a part time co-founder. My other co-founder is working full time on the company, but did not when we originally started the company. In the beginning we were 50/50 but now we agreed to redo the equity split to be fair. My background is in engineering (3yr exp in Mechanical, now currently 1.5 yr exp in software), although we contract out a good portion of the work so I oversee the technical aspects and also pick up work when we are in a rush. My partner's background is in product (5 yr exp). We estimated that he works around twice as much as I do (him ~60 hrs/wk, me ~30hrs/wk).When we had this discussion, he showed me a presentation he put together doing all these calculations of what his "hourly rate" is compared to my "hourly rate", his lost wages (money he could be making if he were working), my "pro's" as a co-founder, my "cons" as a co-founder. He has ~100k to invest into the business where I only have ~30k to invest. Anyway, after all this he came up with offering my 19%. Also worth mentioning that I fit the target demographic of the customer, so I can sell to them way better than he can. Without giving it away, him running the company alone would be like a cat running a company that's meant for dogs.I am an engineer, so trust me I value data and numbers... but this whole calculation plus my "pros" and "cons" just feels petty to me. Including my job, I am working around 14-16 hrs per day (I understand me working for my fulltime job doesn't add anything to the company) which is definitely stressful on me and for 19% just almost doesn't feel worth it.I want to do whatever is fair, so if the 19% is truly fair then I need to evaluate if it's worth it to me. If it's not fair, then I would push back. see hubwealthy.com/wealthy