I think the biggest adjustment is with the putter. For every other club these players can get used to it very quickly.
I respectfully disagree. It's actually the opposite. If the adjustment to a new putter was that big a deal, why do so many players on all tours regularly change putters? The fact is, more players change putters regularly than any other club. If the adjustment was so tough, they wouldn't be doing it from one tournament round to the next--not when so much money is on the line.
Getting used to a new driver takes some time, as do new wedges. But a whole new set of irons is by far the most difficult change to make. This is shown by the fact that wedges and drivers, along with other woods, are experimented with pretty regularly, sometimes even during tournament play. Putters may be changed a number of times in four days. But rarely do you see irons get changed without it taking weeks or months for the adjustment to be made. **That's why I've been using the same Titleist DCI Blacks for the last 16 years!!!!!