Wait. My understanding of the lore is our inability to summon Ramuh had nothing to do with how many Egis we had but rather the primal Ramuh. Primals have different levels of power and it seems different levels of potential power. Having unsummoned Egis doesn't drain you of power. The issue is summoning them in the first place. We couldn't summon a Ramuh Egi because summoning a Ramuh Egi required more Aether than we had. Same reason we wouldn't be able to summon a Bahamut Egi. The WoL simply lacks the Aetheric reserves to summon an Egi of a Primal that powerful. That also means that Ramuh is more powerful than Titan, Ifrit and Garuda but I can believe that.
As for explaining us being able to summon stronger Egis, it would be easy to explain, particularly since research into Allag Summoners was far from over. Potentially their may be a way to perform a more efficient summoning ritual, it might require some form of special equipment such as supercharging our soulstone or it could simply be that we have grown stronger. Don't forget there is precedence in lore where the Ascian fused several of Tristan's soulstones together to allow him to summon Belias Egi.
I can see why they wouldn't go with such a model in this game though. It would be too restrictive to the class as effectively its just a Job that revolves entirely around big burst CDs. Balancing those and making them effectively impressive would be difficult in FF14's combat system. They would have to be a DPS class and to accommodate making those Summons impressively destructive enough the Summoner would be quite weak without them. This would in particular be an issue in fights where mechanically timing the Summon CDs was difficult and if fights where big burst was needed Summoners might be viewed as mandatory. Further they would be a nightmare to balance between PvE and PvP.
Its the same reason that if we ever get Blue Mage, its not going to be the old style blue mage. What worked in FF11's combat system wont necessarily work in FF14.