Mechanized Grenadier Group can be replaced by the 250 in infatry or have lower CP and come with a unique squad like Panzerfusiliers/Volkgrenadeir or the 6 mean repair squad from campaign.
I like the idea of a unique squad as the Mechanized Group - as it stands getting a vanilla Grenadier (even with "Free" LMG) isn't too exciting and as said above - comes too late and doesn't make sense delaying your build order just to get a 250 and Grenadier you could build from Tier 1 anyway. A unique squad would make it worth to make a build order that worked the Mechanized Group into it. Bonus points if the squad would promote combined arms light vehicle play to be thematic.