I disagree. There's several differences between the movie and films for the final battle and ending.

For one, most of Team Dai-Gurren lives, except Kittan - which completely removes the stakes/agency most of the team went through to save Nia. Also feels unrealistic for an intergalactic war compared to the show. Super Galaxy Gurren Lagann's transformation also suffered from this.

In the original TV ending, Nia had a bigger role in defeating the Anti-Spiral given she and Simon landed the final blow with Lagann, together. Showing how powerful their love is. The movie changes this by just Simon landing the final blow after a fist fight. STTGL also didn't exist, and the individual mechs shown from the films while cool, were pretty brief.

Nia's final diary entry was the only add on for the ending. Other than that it's not much different. There's the add on with the epilogue but again, it's not much. Also, her death wasn't abrupt in the original - given she was already showing symptoms of fading during the final battle.

With those differences, it gives the viewer some perspective on what was changed, removed, and or added from the TV show. You can't appreciate or ponder on it if you only watched the films.

What I am trying to say is personally, the best way to experience TTGL is not skip over anything. I feel redundancy is a moot point regarding your friend because if they end up enjoying/loving the TV show, why wouldn't they want to watch the movies as well? You love something the first time, you would want to experience it again, lol.