I see what you mean. Yet even then I guess its just about the way you build the party. For me going 2 sorcerers and 2 wizards is a bit extreme - its pushing the limits and even then I'm not a 100% sure it couldn't work using the right spells. But sub-optimal builds are always there and will have their issues. But like those you meantioned druids and clerics are already capable to be even front line tanks. A well distributed list of spells can also solve a lot of issues or in a primary fighter group the one or the other healing ability completely replace the need for clerics. So overall you can push it pretty far especially with some optimization. But any half-way 'balanced' list will most likely work pretty well without any need to go min-maxing - which is quite an achievement for a system
