Not all recipes are the same. Some ratios are different, yielding a different taste.
Also, and this is a huge factor... using cheap butter will make an unpleasant butter flavor.
All store butters, including Plugra at $10.00/lb, and Land O' Lakes, have natural ingredients added. If you research this, it's a controversial practice in many foods, with manufacturers coming under attack.
Natural flavor means that the compound is made up of things found in nature, but chemically changed and used as a food additive. In butter, for example, it may be ingredients not even remotely related to the dairy industry. These additives are flavor enhancers. They are bolder in cheaper butters because they are substandard ingredients to begin with.
These cheap off-brand butters, because of the additives, will make a buttercream too buttery, just like the salt will bring out a more buttery taste.
I had a wonderful IMBC, but have honed it into an even more neutral taste for flavors from vanilla to Absinthe. The SMBC is the same. FBC still has a bold flavor because the yolks are so rich. GBC is the most neutral.
Another option is to get fresh churned butter from your local dairy or farm market. The ingredient label will only read, "cream", or "milk". But you still must have a balanced arsenal of Eurpean buttercream recipes.
Another issue: The flavor quality you use flavor the buttercream will have a substantial impact on the final flavor. European buttercreams with cheap or artificial extracts or flavorings will have a less-than-optimal taste.