Sosa just had a drawish fight (I didn't see it as a shameless robbery) with the ghost of Gamboa. Neither Fortuna nor Smith are good fighters (and Sosa had to come from behind and pull off a late KO to beat him). He doesn't meet the threshold of "good" in the sense that "good" is a meaningful term at the elite levels of boxing.
As for Walters, I think he does likely qualify as "good", but he didn't look particularly good in last two outings before fighting Lomachenko. He was briefly considered as potentially a p4p fighter after stopping Donaire, but his stock had clearly dropped since then and he wasn't in the conversation by the time he fought Lomachenko after a year long layoff.
Marriaga was a smallish FW without any notable accomplishments who was brought up to SFW. It's an irrelevant win for a fighter of Lomachenko's standing.
This is excessively critical.
The majority thought the Sosa-Gamboa result was a robbery. Anyone can look it up and see. Gamboa is past prime for sure but he still looks alright.
Sosa still KO'd both Fortuna and Smith to prove he is a modern era belt holder. For me, good fighters are B graders, very good fighters are B+ to A- and elite fighers are A, and the very best are A+ ...that's just the general way I see it.
His stock had dropped then because he was robbed of a victory against Sosa and people didn't know who Sosa was, but in hindsight, the competitive but clear victory looks better now. Lomachenko fought him when he was seen as a potentially P4P fighter and Sosa is a tricky, stocky fighter who's not easy to land clean on.
'Year long layoff' - people go O.T.T when discussing the inactivity. It was 11 months and that isn't a scary amount of time away from the ring at all.
'Smallish FW' - this is all semantics which holds no water to someone who has watched him fight before Valdez and Loma. He is a good sized FW who didn't look too small to be in the ring at all with Loma. But you didn't comment on the fact that he did have a razor close fight with Valdez.
There's a purpose behind yo being excessively negative view on these fighters. I'm not sure why that is. Maybe it's a reaction to people saying Loma is TBE when he hasn't proven himself at the highest level yet.
Marriaga to me is B grade. BUT he win is a B- though because it wasn't at his best weight.
Walters strikes me as A- ...the world felt that when he was on his run, he was A grade...and maybe he is...who knows.
Sosa is a regular B grader.