I think it's kind of an unintentional blessing that Tamaki was increasingly moved into the background. Expecting a strong character arc seems like it's asking too much; hiding her in the background is about as good as can be expected, insofar as it seems to explain the much reduced rate of LLL uses later in the season.
I do think Fire Force deserved a second season, despite its many problems, so I'm glad to see it got extended. I hope whichever characters they choose to focus on are handled with a little more substance going forward. It's a very pretty show --- just needs a bit more effort on the main cast's personalities, motivations, & development to make it quite good.