1) You returned a laptop because one of the SSD's reported 730MBps and the other was at 780MBps?
Your real world experience would be THE SAME on both drives. I'm surprised they would even take the laptop back.
*Reasons the SSD performance between slow and fast SSD's can be similar includes:
a) bottleneck may be CPU or other component (or software)
b) System memory (i.e. DDR sticks) hold data for Windows and other programs already.
In the past when I'd start up a program like Microsoft Word it might take a few seconds to open (years ago). Then, if I closed it and opened it again it was much faster. The reason was because the data on the HDD had been loaded into the much faster system memory.
Modern OS's like Windows 10 learn how you use your computer and will preload data, even if you have an SSD, for faster access. It's not perfect, but it's much better than in the past and again one reason why a faster SSD starts to be superfluous.
2) Again, it may not even be the SSD itself.
3) SSD wearing->
The memory has a finite number of writes as mentioned already. The SSD firmware keeps track of this and simply blocks off that memory once it's been written too often thus the capacity of the SSD diminishes.
However, modern SSD's will occasionally MOVE data from parts of the SSD to other drives to more EVENLY spread out the writing so the total capacity doesn't change much until the entire SSD has been well used.
*You can state the number of writes a black can handle, but it's more meaningful to say how many GB's or TB's an SSD drive can handle because again it can be thought of as wearing out roughly the same.
4) Performance->
It's actually a complicated subject. How well it maintains performance depends on the design of the SSD. Things like garbage collection.
5) Firmware update->
Check and see if software to manage the Liteon exists which may include checking automatically for an update. If not, try to manually find an update which may or may not exist.
Link:
http://www.howtogeek.com/165542/why-solid-state-drives-slow-down-as-you-fill-them-up/
SUMMARY:
*To be clear, sending back a laptop solely because of such a small difference in laptop performance is not a good idea; if it's not actually broken then you've just wasted your time, possibly some money, and may even get a refurbished laptop. It's hard to know the exact reason of the difference which again may or may not be the SSD.
When we talk about degraded performance then usually it's a HUGE drop which happens over time. Modern SSD's are usually good at correcting for this, and in extreme cases there are ways to do a SECURE ERASE of the SSD and get back some performance.
**Even then, if it's still quite fast chances are you will see no obvious benefit. If your SSD suddenly became HALF the speed it would be difficult to see much real-world difference.