The issue with the wall is clearly a case of changing common property without the correct permissions. You could explain to your committee that you have the option to take them to the Tribunal to resolve the situation if they don’t tell the builder to fix it or compensate you for the loss.
The fact that this is extra work for the builder is not your problem.
Regarding the tenant, if they demand a rent reduction, negotiate a reasonable figure and then charge that back to the strata scheme. It might be better to involve a third party like a real estate agent or a Fair Trading mediator, if only to establish that the figure is reasonable. I have heard of landlords encouraging their tenants to take them to Fair Trading, just to establish a figure that the strata scheme can’t easily reject.