Brake pad life & LOF brakes

I fitted new callipers discs and pads a year ago to the rear of my 90;
Calipers RTC5889 and WM600071L from paddocks
pads STC9188M

I've only driven about 4k miles, say 5k just on the liberal side, but the pads need replaced. I have also noted that they are wearing uneven - inside face is almost totally gone but outside has some material left (see photo). I have only checked one caliper so far.

1) 5k miles seems very little for pads to be replaced? Towing maybe accounts for about 200 miles of the 5k. Loading, only ever two of us with camping gear and roof tent.
2) I got the mintex pads thinking "dont get the cheapest". Is there really a difference?
3) Is uneven wear normal? New callipers so wouldn't expect piston failure. I have bled the brakes a lot recently, so they've had at least 1L of fluid through them and no air.
4) Considering upgrading, to say LOF power spec. is it worth it?

I did some maintenance on my MY12 puma at the start of lockdown to investigate a squeal from the passenger side rear wheel. It was still on its original discs (brembo) and pads (AP Lockheed with ferodo friction material) and had done 44k miles. All 4 discs had minimal wear and just needed a clean up. Front and rear pads had virtually no reduction in thickness but rear pads were crumbling (hence the squeal). Choice of new pads varied in cost depending on brand starting at under £10 for an axle set. I decided to go for the LOF road spec at about £40 making them one of the most expensive (except for genuine LR in a LR box which are about twice that). The LOF ones came with the pins, springs, backing shims and a sachet of brake grease whereas the others did not. Too early to tell what life span they have but they work fine. I based my choice on "you get what you pay for" but also on the pad friction material which meets the original Ferodo specification which was chosen by LR.

I had sort of similar on my 110 and one of the thin metal caliper piston seal ring had come out of position and was jamming the piston out causing pad wear on one side. No tell tale signs it had happened and only discovered it when investigating a hub leak.

I'm away to do my hubs, discs and pads, so I'll have a good check of the callipers when I do that and order up replacement pistons and seals if required...

Remove one pad a at a time, get someone to pump the pedal a few times until the piston is out an extra 1/2 inch or so, check/clean pistons, apply a few drops of brake fluid as lube and push the pistons back in ( wipe off excess fluid) refit that pad and onto the next one and so on, then fit the cheapest pads money can buy and see how you get on.

Rear brakes practially do nowt on the 90 models and normally rust away if car lightly used, 5k for pads is bad.
That caliper certainly looks a lot older than 12 mths, do you do much off roading etc?

The dirt cheap calipers off ebay and all the ususal suppliers are actually very good value at 25 quid each.