There is not much torque until over 2,200 RPM.
I usually shift at 2,000rpm 1,2,3.. and if at 25mph stay in 4. at 30 speed limit I cheat to 32 mph so i can go into 5th. This is wanting max fuel economy and not any even staying with traffic accelerating..
You may be used to a bigger engine where you can expect a bit of torque at 1,500 to 1,800 or so. NOT on the Mk3 Focus!!
I would say what you experience is totally normal for so small an engine.
When I am wanting to go in a bit more hurry... (driving like the rest of traffic does acceleration-wise) I will rev her up to 3,000 so it has some torque available.
When I want to REALLY go fast I wind her out to 6,500 before shifting.. that is when you can see this car can actually move fast (enough).
Most of the time at 1,500rpm or under 2,000 there is no 'step on the gas and go (anywhere faster..) You have to actually downshift if you want to move smartly.
So, from another lifetime manual driver (47 years driving)
It is not a problem with the engine/clutch.
You just expect way too much at the low RPM you are shifting at!!!
If you ever drove a typical, historical Honda engine?.. This car engine is way more like a typical Honda. no torque, needs revs to move.. Not like a Mustang.
It IS good enough to be a MPG miser using low RPM like you are.. But it cannot accelerate much more them a crawl using low RPM shifts.. Great for MPG.. bad for getting anywhere fast.
So i say rev her up to minimum 2,000 RPM to shift from 1,2,3 and only if stuck in a 25mph zone go to 4th.. for 30 mph it is pretty iffy to stay in fifth.. unless you can be on a flat road, no need to accelerate at all. 32 is minimum for 5th for me.. (I have a mile long flat bridge i can do 5th at 30mph.. but that is zero traffic.. and no headwind either..)
Hope this helps..