Galvis is easily good enough to start at SS on a winning team.
If you look at any 100 WIN team, you're not going to find 8 starters all of which are 4-5 WAR players.
You'll find 4-5 guys who are in that range, 2-3 in the 2-3 WAR range, and 1-2 "weak spot" starters, and a couple bench contributors above replacement
Same with SPs, probably 3 good to very good starters, and 3 who are above replacement, and 2-3 RPs who are above replacement.
The key for winning teams is not only to have a half dozen or so core players, but the depth to avoid playing below replacement players for extended periods.
So in that context Galvis is fine, sure, you'd like Crawford to become a 4-5 WAR starting SS, like any position, you want to upgrade.
But right now the best players on this team are Hernandez, Altherr, Galvis and Herrera (ignoring Kendrick and Nava).
So focus on upgrading the rest of the team (turn Franco around, Williams in LF, get Joseph to step up or replace him, hope Knapp is the answer at C, get the young SPs on track).