Puccini almost always handled this better - whether Rodolfo or Mimi or Tosca or Scarpia or Musetta or Mario etc etc, they get to enter, sing for a bit, and finally get to their first big arias after they have had a chance to get their sea legs so to speak.
Not Mario. Look at how little he sings before "Recondita Armonia." ;-) (Also compare with other composers - Verdi, for instance, who has Radames sing his huge and difficult aria right away, etc. It's not as uncommon as you may think.)
Anyone can ostensibly sing about "life and art" etc. But in Tosca's aria, "I lived for art and love" isn't really a motif, it's just a starting thought that really don't get developed - the aria itself is a plea to god in a horrible situation, it's NOT about her being an artist (whereas Adriana's aria, sung in the context of her practicing her lines, is.) Tosca is really singing more about "I've really tried to do so much good in my life - how the hell have I ended up here?" I think you're making way too much of one single lyric, lol. Might as well compare "Poveri fiori" to Don Jose's Flower Song - hey, they both have a flower motif...;-)