Older alternators took a big drag on the starter and battery when cold starting. An alternator can take from 5 to 10hp depending on size of course. That is a lot of drag for a starter motor to turn when cold starting. A starter motor can also be made smaller as there is less drag from the engine.
I believe newer alternators delay charging until the engine has started. How is this done? By external electronics or incorporated in the alternator? If in the alternator then a replacement would benefit an older engine.