Everything you just said is false and there is zero evidence for it. They are just wild assertions that you are regurgitating.We do gain function. Look at the example of eyes I gave. But you can do that with anything. Every single thing that works in our body is gained function. Species both lose and gain features as needed. Whales are mammals that went back into the water and regained fins for swimming. Clear gain of function.
Our ancestor species no longer needed their tails for balancing on tree branches as they moved from an arboreal to a terrestrial lifestyle so we lost them.
There is no fossil evidence that supports that species became extinct through the competition that Darwin insists is necessary for the emergence of new and improved species. You see, to “create” new species by evolution, the older species must become extinct or at least separated geographically. So evolution is also a concept of extinction of species. But there is no fossil evidence supporting extinction of any species by competition with the new and improved creature.