Yes, for 100K files main problem is algorithm complexity, for Similarity it's N^2. That means for 1000 files it takes 1000^2 = 10^6 ephemeral units of time, 100000 files it takes 100000^2 = 10^10 ephemeral units of time, difference 10000 times, not 100 as for linear complexity. Very big speed improvement can be achieved by duration check, it skips many unnecessary comparisons, but complexity still N^2.
We working right now on 4th algorithm (in truth 5th, Similarity already have 4 audio algorithms, 2 of them just mixed by name "precise" one for long songs, one for short), it must have linear complexity, but work still in progress, we don't think we can release it in next version.
In current versions better solution to limit comparison areas by limiting selected folders or using folder groups and cleaning/moving cache.