Watson, returning from a calf injury which had kept him out of international action since Boxing Day, struck 122 off 111 balls in Canberra to guide the hosts to a 39-run victory in the third one-dayer that secured an unassailable 3-0 lead with two matches of the series remaining.
Phil Hughes (86) and George Bailey (44) also weighed in as Australia racked up 329-7 before bowling the tourists out for 290 in 47.3 overs, but it was Watson's ton that caught Harvey's eye.
"It's great to see him back at the top of the order for Australia because I do think they've missed him," the former Baggy Greens all-rounder told Sky Sports.
"It's so hard for a captain to set a field for someone like Shane Watson because he hits all around the ground. If you drop a fraction short he can still get on that front foot and pull you away and if you get up full he drives you and hits you back over the top of your head."
The West Indies' chase was well-placed as Darren Bravo (86) and Dwayne Bravo (51) guided the score to 195-2 inside 35 overs after Kieran Powell had struck a swift 47.
But the innings faltered when both fell in the space of 20 runs, together with the wicket of skipper Chris Gayle, who batted down the order at five after sustaining a side strain in the field.
"There were a lot of starts but no-one went on with it," reflected Harvey. "Gayle had to come in lower down the order and that really hindered them at the top of the order.
"Devon Thomas  did a fairly decent job coming up after he got knocked on the thumb while wicket-keeping but I still think they missed the presence of Gayle at the top.
"They'll be disappointed because they did get a lot of starts - they just needed someone to go on and play that Watson role and get that hundred, which the other batters could then bat around."
Left-arm seamer James Faulkner bagged the wickets of both Darren Bravo and Gayle on his way to figures of 4-48 from 8.3 overs.
But with a four-Test series against India starting on February 22, Harvey was impressed with how the Australian attack worked as a unit.
"That was a good examination for the Australian bowlers," he said. "The ball didn't swing anywhere near as much as it did in the first couple of ODIs in Perth.
"So it was good to see how they reacted. I think they may have overdone the slower ball today but they had to try different things.
"A lot of these bowlers will be off to India shortly and they are going to play on wickets where the ball won't swing as much and they are going to have to come up with different ways of not only trying to get batsmen out but trying to stem the run flow."
Watch the fourth one-day international between Australia and West Indies, live on Sky Sports 2 HD from 3am on Friday.