I don't know anything about US community colleges. Or... I can't remember what they are called... Undergrad only institutions (e.g., Tufts).

Generally... A US degree is 4 years long. You have a depth requirement (to do with your major) and you have a breadth requirement. US degrees have a greater breadth requirement so if you are a science major you might well be expected to take some arts papers and / or have a language requirement. If you are an arts major you might well find yourself with a mathematics requirement.

There are 'upper level' courses (more to do with your major) and 'lower level' courses (more general / entry level).

A degree in the British system is standardly 3 years long. The breadth requirement is less so you don't (typically) have a maths requirement unless you are doing something that specifically needs it or have a language requirement. Some UK degrees are 4 years (e.g., law, engineering) - but that is not the norm. And law isn't an undergrad degree at all in the US, it is a graduate entry only degree...

There are 'stage 1' 'stage 2' and 'stage 3' courses and they get progressively harder / more specialised.

If you want to go on to PhD then you need to take a 4th year that is very specialised indeed... It is basically course work / research at a level that early level PhD students would be doing in the US.

In the US a PhD is standardly 5 years. 3 years of 'generalist' knowledge for your field (a breadth requirement, again). It is around the level of honours specialist coursework in the UK system. Then you have a thesis that you get around 3 years to write. In the UK system you have thesis only PhD programs (which is sometimes why people arrange to visit a US institution for a year of coursework).

So the main difference is length of time taken. And the bulk of the difference is in breadth / generalist requirements.

Does it turn out better specialists?

Hard to say. Pros and cons for each. More time to figure out what you like if you don't know. More hoops of stuff you don't like if you already know. It might give you more information to be thinking laterally with... On the other hand if you are part of a good research institution then attending specialist seminars by people working in other areas of the field will basically do the same job.