The Pikey Life

[nominous]

In general house prices are consistently increasing, the problem with renting whilst saving for a house is that the house you would like to buy will be getting more expensive by the day.

In general historically, house price rises have always been followed by a massive drop and a bust situation with lots of people having to give up their homes.
Up till 2008 that was generally the way people thought and certainly the way the housing market had operated.
2008 taught us that you can't expect the status quo.

Take a 95% mortgage with a slightly elevated interest rate fix for 2 years

And take the risk that during your fixed rate the interest rate goes up dramatically (remember not 6 months ago oil was still very high and we had inflation, BoE was talking about interest rate rises) after your period ends and you don't have a high enough LTV to get a better rate. Thus your monthly payments go up.
It depends how much one stretches the monthly budget to get that 95% mortgage of course.
Point is that there is a down side related to affordability and it's clear that up to 2008 many people (generally those taking 95% mortgages and above) didn't think about affordability and the consequences.
It's not just cut and dry rent verses buy even if there are the same costs today. There are other factors to (should) consider.

My mortgage cost is equivalent to the rent I would be paying if I had chosen option 2, so with the money I would've been saving I am instead overpaying my mortgage to ensure I have a better LTV when my 2 year fix is up.

Which itself makes makes a lot of sense. However the 12% rise you've seen is not something you could have predicted. Wit the benefit of hindsight you've made the right decision, but at the time you could not have predicted a 12% rise, just as you cannot predicate what will happen in the next 15 months.
Given the rise you've seen it should hopefully result in a better LTV in 15 months time. Hopefully interest rates will still be low and house price deflation isn't taking place.
But your LTV still wont be into the sweet spot of 75-80% mortgage deals so you'll still be paying higher rates.
Plus the banks make take a dim view on highly leveraged property (due to current economic situation at that time) and despite whatever the base rate is, may further load the higher LTV because they see a bigger risk - again something that you cannot predict wont happen.

In general I think you should get on the property ladder as soon as possible, even if you can only scrape together a 5% deposit.

All folks circumstances are different. It's also got a lo to do with how you assess the potential risk and affordability if XYZ should take place and you either need to sell up or cannot afford to repay.

It's not just a cut and dry situation rent or buy.
One should weigh up not just what is best today, but what one feels the future holds and base such decisions on a forward outlook for 2,5,10 years time.