A couple of things.
Re: "no definition of takeoff flap" - there probably is such a definition, explicit or implied, in the Airplane Flight Manual; you can't read the TCDS in isolation.
re Stall speed effect on VMC. There's nothing explicit in the regulations linking VMC and Vs - they both then impact operational speeds independently. But there is an effect of the lifting capability of the wing on VMC - simply, if you can't maintain level flight you can't demonstrate VMC, and it was all about demonstration back then. So even if there is theoretically enough control power at lower speeds, you can't have a VMC below a certain speed, regardless.
re flaps effect on VMC - there's also (sometimes) a directional stability effect of having flaps down (more flaps = more directional stability) - this then can help in a VMC condition as the helping effect of directional stability is why the bank into the live engine is helping. So a higher VMC with less flaps could work.