Hi Terry,
Good to see you are also still alive.
This is an area that I have been working on both on the erg and in the boat, in my case it is trying to 'unlearn' something I was taught as a junior.
As a junior I was taught to take the initial drive with by back, to place my shoulders behind my hips and then drive the legs with a straight back, the idea being that the main leg drive was then against a solid spine, rather than a bent one, this aproach also prevents 'shooting the slide' or 'bum shoving' as it is known over here ;o)
More recently I have been told to keep rocked over and drive whilst still in that position and only open up at the end of the stroke.
My main criticism of this 'new' method is that it can promote 'bum shoving' if not done right, I was quite vocal to our coach about this.
In your first video I can see you opening up quite early and largely rowing like I describe how I was taught as a junior, although slightly less pronounced than I was, I would still class this as a pretty good stroke.
In your second video you have some serious 'slide shooting' happening which is largely wasting your legs and then putting a huge strain on your back and relying on your upper body for the majority of the stroke.
To be fair, you improve a lot by the end of this second video, but you are still losing most of the power from leg drive and having to finish the stroke with way more upper body than you should have to.
The 'drive while rocked over' only works if you have a strong core as you need to keep your entire body 'locked' while you perform the drive part in order to avoid shooting the slide.
Initially it may feel like you are placing way more pressure on your lower spine in order to have a meaningful drive whilst in that rocked over position, but as your core strength increases you will be able to drive the legs and not waste the energy as you will still be taking the oar(s) with you.
This has taken me many months of training to move from one 'style' to the other and believe me I still have a long way to go for it to be second nature.
You can feel/see potentially the progression better on the RowErg as there is no real 'arm action' just a handle on a chain so you can easily see if the handle is moving as a result of leg drive or body movement from a side video perspective.
This is part of the reason our coach has us doing 20 minutes of core exercises after every erg session.