Not driven a Mach-E myself, however watched a lot of videos and have a Polestar.
Mach-E standard range is meant to be very close to the listed value. Where the Polestar is at the moment 2/3rd's of the WLTP (although note it is winter, but even before winter people were complaining range wasn't even near 250+ miles). However we have yet to see the Mach-E in the hands of someone like Bjorn for serious testing ... and the Ford's range is still "nice" condition - not optimal but also not winter!) But I'd say now the Ford has the edge.
As it standards right now I would say that Mach-E has a better Android system than the Polestar, due to standard Android Auto compatibility. However long term in 1+ year I'd put money on Android Automotive - once GM in the US and PSA Group in France (Citroen Renault Peugeot) start rolling all their cars out form 2021, I'm willing to bet a lot of apps will start to appear on Automotive.
In addition a lot of the video's I've watched have some serious lag in the Ford screen. Now the Polestar isn't perfect ... sometimes the seat heaters lag as an example ... but I've seen the Ford Lag on almost any screen. Also a lot of reviewers have said the dial on the Mach-E's Screen feels cheap ... yes it works and feels solid now, but as it's just stuck on the screen how long will this last?
Sound - I'm not expert in sound. There are others here that are perfectionists so maybe they can chine in. However, I've never found a B&O system I liked ... where the HK imho is brilliant.
Also not that the in the RWD-SR the audio is downgraded too. You don't get the 10 speaker B&O.
Seats - Both the base Polestar and Mach-E have non-ventilated seats. You can upgrade the Polestar but not the Ford. Most people don't have a problem with this, but there are a few that have reported sweating in the seats on the long drives.
The Polestar has Heated Front and Rear seats, where the Ford only has Front.
The Ford has 8 way configurable seats, where the Polestar has 14 way (although cushion exertions are manual and not power assisted). Although note that the RWD-SR is manually adjustable seats only.
However, they both come down to a personal taste and whether you can find a good driving position.
The Mach-E seems like a very good car overall. The RWD Long Range Model is more comparable to the Polestar 2, as they are closer in spec as well as cost but if you are comparing the RWD-SR to the Polestar, the P*2 is more expensive but you have more tech as standard.
The Polestar feels more luxurious inside and has AWD compared to RWD only (yes you can upgrade the Mach-E but then you are not comparing similar costs)
The Ford seems more practical with a bigger Frunk and Boot. Although the final version does have some dividers in the Frunk for some reason - not sure if you can (or should) remove these.
Also note the RWD & AWD SR Models only charge up to 115kW and not 150kW as per the LR variants and Polestar.
The Polestar is faster and more a "drivers" car.
So conclusion : IMHO if you need a practical family car the Mach-E might be a better option. Where if you want a more drivers focused car then the Polestar 2.
Also you asked about the LR & SR version. However I'd look more into RWD vs AWD. If you don't really need AWD (i.e you are not going to really off road it) ... then imho the RWD - LR is a good car, but unless you are leasing I'd be concerned about residuals long term ... therefore the RWD-SR seems like good value.
There are different Spec's in all 4 cars even though they almost all look the same, make sure you get the car that suits your real needs - don't think range is everything. I don't know how many miles you drive, but even the Polestars 200 miles in winter has been more than enough for me and my family to travel around the UK.
One final note: We now know all the Polestar's gremlins, quirks and features. The Ford is a still big unknown.
The other side has the MME SR and the Kia. While the Kia has a longer range, it charges much more slowly so you're stuck on the side of the road a lot. The MME SR needs 2 more charging stops. It needs 7, all the other just 5. They are both about 1h30min slower. Bang in the middle comes the Polestar, at about half an hour slower than the faster cars, so 1 hour faster than the slow ones. So in (simulated) practice, it's not an issue except with the Kia and the standard range Mustang.