Qualcomm still are the only relevant ones in town who actually sell high performance ARM designs to third parties and have no political quarrels attached, there's a lot of money to be made in that game.

As you said there is competition from Mediatek, but who knows how long Mediatek has before the US government sanctions them to hell and beyond. Apple doesn't sell to third parties (no matter how much one might dream) and so does Google. Samsung I haven't ever seen used outside of their own phones and TVs.

The remainder is NVidia's Tegra lineup but other than automotive and the Nintendo Switch I haven't seen these in third party products either, I doubt they'll even take your calls if you are not coming in with millions of units sold of demand.