Yes if you are comparing to a modern Volvo D5 with common rail direct injection and variable-vane turbo and twin cams and full electronic control, and around DOUBLE the max stock torque output at MUCH lower RPM, it's no surprise this engine may have a different dynamic feel even if it's all working as intended.
Volvo D5 maximum stock torque output:
440nm (325 lb-ft) at
1500 rpm
Volvo D24TIC maximum stock torque output:
250nm (184 lb-ft) at
2400 rpm
They are truly different animals and very much in different worlds in terms of performance and technology.
Turbo failure on a D24T is very rare. As in very, very, very rare. We basically never hear about it here. Most of these engines are running the stock original turbo still after almost 40 years and in some cases a half million miles or more. They pretty much just don't break unless run out of oil or if a failed air cleaner lets a bunch of dirt and sand in. So rebuilding the turbo is probably not the direction you want to be looking just yet.
Much, much more likely that either the engine is running as designed and just isn't on a par with what you are accustomed to, OR, turbo and/or fuel pump need adjustment. "Dangerously slow" and not able to keep up with traffic does sound like something might be off. Here where I live, highway traffic generally moves at 90 mph or more, and the engines in my old Volvos (even the lower tune non-IC D24T we have here) are perfectly happy to do 90-100 in order to stay with other vehicles. The only reason I don't do that is that the rest of the 40-year-old car containing the engine doesn't feel safe at those speeds.
If yours struggles to move with traffic then perhaps you have an issue with turbo output, or more probable, the injection pump timing is incorrect from a sloppily executed timing belt or IP replacement in the past.
Should start with measuring turbo boost as you have planned, and continuing the "Stage 0" maintenance you have already begun, focusing on a full and perfectly executed timing belt service (including water pump and thermostat) and ensuring all the fuel pump and transmission adjustment settings are spot on. Then later once everything is running as intended, you can certainly increase turbo boost and fueling settings above stock, as that can yield good further power increases and your car already having an intercooler is able to take advantage of more fuel and air quite easily. ASSUMING the cooling system is in healthy condition to safely exhaust the added waste heat from increased power.
Another way to check your car's performance: Could you find another antique Volvo turbodiesel to drive and compare yours to? Maybe meet forum member jpliddy and try out his car if he is not too far from you?