IIRC, the BJ-O was not that widely spread when it came out in '58 but the Apollo came out in TRO3055 . . . and that was the book that covered the IS response to the Clans.
Forget that it was probably cheaper and easier to produce to start replacing losses, look where it fits in your strategic picture as a import. Its going to your secondline forces. If I was the AFFC in '51-'55 (it came out in '54) then I have been shuffling the refit kits, heavy mechs and better medium mechs into the Lyran zone to face the Clans. Since the Clans have a range advantage, that definitely means the Archers & Crusaders I can move and likely the JagerMech 6-A even if I am cringing about its thinner armor. So now I have a bunch of 4/6 companies on the CapCon, Periphery and probably the Drac borders that are missing slower missile fire support. I certainly were not replacing them with Dervishes since with the classic trio its a fire support mech that can match the speed of heavier Clan forces. And the AFFC has a lot of 4/6 heavy and medium lances that would have been picked over to bolster the Clan front- all those Enforcers, old Centurions, Jagermechs, Zeus, and other 3025 designs. My new built stuff from former FS factories up to '55 besides the Watchman is being shipped to the OZ border. Lots of new build stuff (from War Dogs to Victor 9Ds) would need some fire support if a Archer/Crusader was not available as the AFFC tries to rebuild the wrecked regiments and later change over outdated equipment in the FS half (you know what ended up in warehouses . . . ).
Also look at the factory it is coming out of . . . Calloway IV which is a half dozen jumps away from the Sarna March means that its going to be easy to pull the before mentioned Archers, Crusaders and Jagermechs out of the SMM, Republican Guard and FC Regular units. They can be moved to the OZ, perhaps even stopping on Hesperus to undergo a refit using the kits. And you can route the smaller replacement into the Capellan March to give a slight upgrade (DHS should let it sustain the fire a Archer 2R spits out) to bring Hasek-Davion's March units back to full strength.