Chef at restaurant seemed to be using really flimsy pans
Are thin-pans totally usable and it's just all in the chef?


Yes, and no. 

As usual, skill matters more than tool choice. A bad cook won't turn out good food with a great pan. A great cook with a bad pan will usually outcook an intermediate cook with a great pan. But the same intermediate cook will turn out better food with a great pan than with a terrible pan. 

The difference the pan makes is mostly the evenness of heating, and somewhat in the food layer which gets heated. A professional cook typically pays more attention to the food and knows how to react to uneven heating, e.g. by stirring/flipping at the best moment. The pan in the professional kitchen is also better preheated, instead of being taken out for the current dish only. In some parts of Europe, the home cook also cooks on a resistive stove, so each dent or warp is very problematic, unlike cooking on gas. 

Then there come the cooking techniques. The thin pan limits you there. It is well suited for standard frying and stir frying. That is, you use enough oil and keep the food moving. Many home cooks love to apply an almost imperceptible amount of oil, which means that the pan's heating evenness is much more important. Also, if you want to leave your food sitting there, an overheated pan (or a pan with overheated spots) will burn it. 

There are also results which I think not even a pro can achieve with thin steel pans. For example, I have never seen crepes get a beautiful even dark color when made on a thin alu pan, while mine get it automatically in the cast iron at home. 

In the end, your purchasing habit is your personal decision. A thin pan is not equivalent to a thick pan in handling and outcome, and it is up to you to choose what tradeoffs you are willing to make.