Yeah never take anything less than a 50/50 split. During the initial fundraising rounds (seed, Series A and maybe even into B) you're also going to be doing just as much lifting trying to get a deal done while also doing your regular day-to-day engineering responsibilities. Maybe in a world where it's 3 founders you can side-step this responsibility but at point you're not just the CTO you're also the de facto COO while your partners are trying to get a deal done.