Perhaps a better option would be a split buy. Three F-105 based frigates now ... and further down the track maybe 6 Type 26 frigates.
I'm badly averse to the idea of such a split. It just adds another major change midstream, with all the added risks that come with changing to manufacturing yet another new (to us) design.
Better that whatever choice is made, the new ships be built in blocks allowing a maturing within the blocks (and the early ships can be updated to match the later within the block to fix early build gremlins), and if needed, a step change between them if for example technological imperatives drive it that way - same ship but more obviously modified like the stretch of the RNs Type 42 batches
The size of batches is an issue too. Consider that if we choose to build the first three as one batch, then change, it's likely that only the first ship is even in commission when number four (second batch) begins construction. And long lead items will have already had to be ordered possibly before ship number one is in service. So how many in a batch to get a feel for what works and what doesn't?
And just how does the Navy decide what is wrong with the first batch on zero actual experience? I suspect that within this forum, the answer is "does it look as cool as this new design, and does it do what the new design promises". If it doesn't, change to the new design.
I call this the iPhone technique. Keep changing to the latest, whether it's a genuine improvement or not, and that's fine if you're paying for it, or own the manufacturer and make a profit. But this taxpayer owns a tiny bit of the government's debt, but doesn't mind a sensible use of his taxes; however I would look very hard at a politician that allowed changes that don't meet the common sense test.
oldsig