If it was available in the same range of sizes as standard radiators, at the same price point, then maybe sometimes. But an increasing amount of my work now is in the retrofit air source heat pump market, where we need higher flow rates due to the reduced temperature difference between flow & return. 15mm compression valves are often unsuitable as you just can't push water through them fast enough without them getting unacceptably noisy, so we end up using ¾" union valves instead. Radiators with fixed 15mm compression tails couldn't be used in that scenario.