A very good question. There are many things to consider here LC, and base gravy isn't where I'd normally use GM, but some do, and I have done.
Garam Masala is just another Mixed Powder.
A mixed powder can be anything it needs to be. A simple 4 spice blend of T,C,C and C or 24 spices in a version of Kitchen King. Or anything in between. Abdul's 8 or my derived 5432211. I cook my breakfast scrambled eggs with just Turmeric and Kashmiri Chilli, but I could use MDH Kitchen King. I probably will now just to see what it's like.

My first question would be, which Garam Masala did or do you use? Is it just the bog standard GM?
My second question is, which spice or spices from that GM do you think is, or are, the problem, and for which dish? Cloves would be the stand out for me, or possibly cardamom. Maybe black pepper.
I make my own blends of GM, as well as buying generic, and have 6 very different Garam Masala blends in my kit just at the moment. Even the bought stuff is a mixture of this and that, old and new, now. Generally I use them as a garnish / enhancer added late in or after cooking, but if I examine a recipe and see that multiple individual spices can easily be replaced by an equivalent portion of one of the GMs, I'll substitute it out simply for ease and efficiency.
As for inclusion in a Base Gravy, horses for courses. For a very neutral base, then probably not. In a gravy for a full flavouried dish, then certainly possible. In my analytical study, I can see the common GM spices show up regularly so it can sometimes be used to reach the same ends. I have also started to use different base gravies for different dishes, which probably isn't true BIR, but it minimises the similarity of all dishes on the table at one time.
From day one here on this forum, Mixed Powder formulae, that include another mixed powder (of unspecified type :ie, curry powder) as an ingredient has frustrated the hing out of me. I've sort of finally come to realise that it doesn't matter too much at all.
