To quote @swamidass
Homoplasy is similarity that is NOT consistent with a tree, and therefore NOT well explained by common ancestry alone. These are the exception to the rule of phylogeny.
Homology is similarity that is consistent with a tree, and therefore well explained by common ancestry alone. These are the rule.
Both Homoplasy and Homology are types of similarity. If common descent were true, we would expect to see mainly Homology, with some Homoplasy, and that is what we see.
BLAST is a way of measuring similarity between sequences, but it does not use a tree to do so. So, effectively, it groups Homoplasy and Homology together and makes no distinction between them.
SIFTER group sequences by a tree, so it tries to ignore Homoplasy and focus on Homology.
If similarity was explained merely by common design for common purposes, we expect BLAST to work better than SIFTER. However, we see that SIFTER works better than BLAST. That is what we expect if common descent is true.
By the way, you were rebutting the argument that more complex stuff evolves from simpler stuff by showing me a picture which includes both myoglobin and haemoglobin, which is evidence more “complex structure” proteins evolve from more “simple structure” proteins.
so what is the chance to get the same function again by convergent evolution for instance?
Have you heard of non-homologous isofunctional enzymes?
[Addit:] Now that I think about it a bit more, I can think of some testable predictions/refutations about non-homologous isofunctional enzymes comparing evolution vs common design regarding phylogeny of kinds and evolutionary optima. Can you think of any?