I don’t know that anyone can judge the “lukewarmness” of a cradle Catholic or anyone else by whether he/she sings loudly or “fellowships” (oh, how I hate that word used as a verb) a lot or not.
The Mass has always been Eucharist-centered, and rightly so. While I might admire someone’s singing voice, that’s not why I go to Mass, and I certainly don’t go in order to go have donuts in the parish hall. Being truly involved in the Mass is very personal, and though I really, really like to sing, and do, (I won’t touch a Marty Haughen or SL Jesuits song though. Even I have my standards.) sometimes I find it distracting, particular when singing starts up while I’m in line for Communion, or when I have returned to my pew.
Not to be unkind, but other than the possibly stem-winding, but possibly boring sermon by the minister, a couple of usually obscure readings and a song here and there (usually fewer than in Catholic churches nowadays) there’s just not a whole lot to most Protestant services, and I can well understand their feeling that perhaps “fellowshipping” is high on the list of reasons for being there.
The kinds of comparisons one often sees are “apples and oranges”. We’re just not doing the same thing when we go to church, and we who are Catholics ought not to try emulating Protestant ways at Mass.
One should not be misled by the Protestant “tithing”. A lot of that is a short-lived phenomenon. If you don’t produce, lots of those churches will eventually ask you not to come back. It’s just a different thing all the way around.
Lest anyone misunderstand, I grew up knowing far more protestants than Catholics; mostly Fundamentalists of one kind or another, and I do admire the faith of many of them. But I’m not too impressed with the “isms”. Neither are lots of them. For a lot of them, the “brand loyalty” is not very strong, and not necessarily long-lasting. Christianity, yes. But whether this kind of Baptist or that kind of Holiness church or non-denom, not necessarily.