I've traveled in all those countries except Kosovo without a rental car. Of course, it depends to some degree on precisely where you plan to go, but Albania (especially) and North Macedonia are difficult without your own wheels. Public transportation mostly means buses, and finding online schedules ahead of time is very challenging. I struggled even to figure out where several bus stations in Albania (usually just parking lots) were located. Misinformation abounded as recently as 2024. As a result, I ended up using a lot of taxis to move from city to city even though I'm a relatively patient and adventurous traveler not averse to communicating via charades. Taxis over long distances aren't particularly cheap, even in low-cost countries. I wouldn't be surprised if Mr. E's approach is more cost-effective, though it requires commitment to a schedule in advance--not the way I travel.
I've read nothing to suggest it's a particular problem to travel by rental car in that part of Europe. I think you'll find rental rates in Albania relatively low. It's important to check ViaMichelin and/or Google Maps for routing info rather than just looking at a map and taking what appear the most direct route. Especially in Albania, there are mountains making the short route sometimes very problematic. My inter-city taxis were arranged on the spot with agreed-upon fees (off-meter). You have to assume the drivers took the fastest prudent route; they often opted for round-about routes.
Note: I don't know about Kosovo, but you are likely to need cash frequently in Albania. ATMs there have high fees. At least in some cities you can find legit money-changing booths that operate on about a 1% margin--far less expensive than ATMs. Euros are preferred, though dollars may also be accepted (perhaps at a somewhat higher mark-up). I wouldn't want to travel with a large wad of cash, but if any of your travel party has leftover euros from earlier trips, divvying up that cash among you (up to what you're comfortable carrying) will probably be helpful.
Alternatively or in addition, you have plenty of time to acquire an ATM card that refunds ATM fees. Charles Schwab still does that. I believe Capital One does not.