As noted, it isn't 60% more. It's also worth pointing out that only for some division types does GB left with max planning damage outperform SF with max planning, even for generic nations. But SF falls off substantially less when its planning bonus declines.and that translates into 60% more max attack - that's far more than any other doctrine, and usually an effective 100% increase or so when you consider the other modifiers you're near-guaranteed to have.
I haven't played new focus tree France, but at least with old focus tree version it took so long to remove the penalties towards doctrine research that it might not have been worth the cost/time to switch, and just leave their doctrine at starting value for crucial '39 conflict. Especially since you could still research equipment and air/naval doctrines normally. In MP what is even viable would depend on ruleset (some don't even allow player France IIRC) and who is playing which nations. For SP you could realistically hold/win by fighting Germany ASAP, or simply waiting until WW2 but beating the AI in the air. Especially before the crazy buff to AA, AI Germany would just get completely shredded by air superiority penalties and CAS bombing in low countries river crossings, taking mostly crits in addition to the CAS damage. Not long before they run out of equipment like that (kind of like what happens to beginning player Germany before they understand the mechanics ).which is why i always push back on people saying france should go gbp. france can already get ~80% planning easy (30 base, 25 protected by maginot, 15+ tassigney fm, 8+ juin general). going from +80% attack to +110% from planning is actually less than what they would get just from the +20% attack on sf, 1.2 * 1.8 = 2.16 > 2.1 which is what max gbp planning is giving.
Neither of those options depended on land doctrine, or even meaningfully used the land doctrine beyond simply using the Maginot max planning to punch through a bit easier. Maybe the new tree makes using land doctrine a bit more feasible, but people are still holding over on old advice?