Some interesting stats here:
https://fbref.com/en/comps/9/keepersadv/Premier-League-Stats
The best stat for comparing keepers is "Post shot expected goals minus goals allowed", which is the number of goals you would expect to be scored from all the shots taken against them (Post shot expected goals) minus how many were actually scored. So negative means the keeper has saved less shots than would be expected and positive means they saved more than expected.
On this stat Grbic is stone dead last in the league, Wes is about a 1/3 of the way down.
The site also lists this stat per 90 mins, which effectively tells you how many goals a keeper is saving you or costing you per game. According to this Grbic is costing us 1 goal PER GAME compared to Wes who cost us 0.06 goals per game.
Obviously Grbic hasn't had many games compared to Wes so you have to take the stats with a pinch of salt, but the consistently baffling technique when facing shots along with the terrible distribution and complete lack of presence in the box makes you wonder how he's got anywhere near any professional football team, let alone La Liga and the Premier League.