as far as you know, becoming a juubi jin cost madara his ability to use susanoo
Nope, It only cost Obito Kamui because he said he couldn't transport the Juubi to the other Dimension and Susanoo does not require doing anything close to that. In fact Madara was able to use Kamui as the Juubi Jin on himself even though it was a different one so to speak. So Juubi Jin Madara's PS would be much more powerful than Sasuke's since he did say Sasuke and Naruto were both half the Sage while he was the whole Sage and even had his own Sharinnegan which again should further powerup his PS since he has 3 eyes and not 2 when 2 eyes are needed originally.
Only, Sasukes Susanoo displayed far better firepower than Madaras PS. Get your facts stright.
Not really, you have to match them as they were on the same level (EMS to EMS). Madara EMS shown to cut thru 2 mountains and said to have the power of destruction comparable to a Bijuu while EMS Sasuke's PS is featless since all it's feat was made from a PS+BSM combination and Naruto's BM chakra alone was giving others a 4x-6x+ power boost (Kakashi first got Kurama chakra and said his Kamui was at least 3x stronger, Naruto made the chakra more powerful and higher in volume when he gave the alliance as said by Kakashi so that's like 4x-6x+ power boost) so BSM power would increase PS power much higher.
We see Sharinnegan's PS being stronger than EMS Madara's Susanoo but Juubi Jin Madara who is a full Sage while Sasuke and Naruto are both half, and have 2 Rinnegans and a Sharinnegan would have a much stronger than it was at EMS. I personally think Kishi could have done a lot better by giving Naruto and Sasuke a good amount of time to train in their respective powerups and chalk it up to a Sage S/T power in the between life and death realm.
Madara's Susano'o wasn't "implied" to be stronger than Sasuke's in any way. To compare the size is misleading.
Oh? Everything Madara showcased as an Edo was much greater than Sasuke; taijutsu, katon jutsus, ninjutsu destructive capabilities, genjutsu (Madara controlled Kurama with only 3 tomoe Sharingan while Sasuke and Itachi said they need the MS for such a feat), battle experiences, knowledge of jutsus, chakra reserves, durability, and love for battle. Madara completely mastered the Sharingan to the highest level, Sasuke lacked mastery of his EMS due to no training and lack of experience with it. MS Sasuke when he went blind mastered his MS far beyond MS Sasuke when he first got it due to him using it in combat over and over and going thru intense emotions in those battles (Sharingan gets stronger in hate which Sasuke was fueled by at that time). EMS Sasuke wasn't fueled by blinding hate nor tried to attack with all he had in the war, which is smart to conserve chakra and not blindly rushing in, but that also meant he didn't know how to fully use his PS which would means less power.
Sharinnegan Sasuke was better with PS but You can't say he would have an as strong or stronger one than Juubi Jin Madara when Sasuke and Naruto are half Sages while Madara is a Whole Sage with 2 Rinnegan and a Sharinnegan with the Juubi's chakra giving him more power.