i've not seen even a cheap SSD slower than a mechanical drive..... slower than better SSD yes, but not slower than a std 5400 drive....
most common issues for drive death are heat and vibration.
1) having changed the drive previously, have you correctly refitted shock mountings..
2) do you keep wandering around with the laptop running, picking it up, putting it down, and so on, while actually using the drive? believe it or not, you're NOT supposed to......
3) is there a motion sensor protection system ? and is it enabled?
4) do you sit with it on a cushion or some such other soft squishy stuff, blocking the air inlet/exhaust from from the case assembly.... causing it to over heat the drive
5) is there a fan assembly for the drive housing ? has it been deformed in your drive replacement activities?
and other related things..... that a little thought and common sense might reveal.
essentially just remember , mechanical drives do not like heat or vibration/motion while in use.... the tolerances inside these things are tiny, so even a relatively slight shock can bounce the heads off the platters during a read/write/seek operation.... causing damage to the platter, and head mechanism, leading to data loss and early failure.
SSD drives are immune to the mechanical aspects, and more tolerant of heat.... (although it can still cause failure) , and most are typically faster than the average mechanical drive.
but cost a whole lot more as well !