Wingull is potentially suspect worthy because it forces an unusual amount of 50/50s from the sheer threat of its one time nuke (and lack of reliability afterward), as well as nearly perfect coverage between its STABs. It's not outright broken in the sense that it will not usually cause a competent non-user to have a lower chance at winning; however, it's viable enough to have a serious impact in the average game and matchup, and does not have an unacceptable opportunity cost to use. This means if the degree to which it forces 50/50s is severe enough, it should be worth considering for a suspect as opposed to, say, confusion or Baton Pass.

The biggest reason as to why Wingull forces so many coinflips is that a standard set of Scald/Hurricane/Protect/Roost lacks totally reliable counterplay, similar to Zoroark in gen 6 RU. The average amount of damage that Wingull will cause isn't greater than other offensive threats, which is why Wingull isn't flat out too powerful. The issue is the -potential- damage it's able to cause against an opponent who is both
a) reasonably well prepared for Wingull from a teambuilding perspective, and
b) does not make suboptimal plays against it.
This becomes an issue of uncompetitiveness only starting at a medium level of play, so it's not as bad as Swagplay in that sense. Past that point, Wingull often limits the available plays to 2 or 3 with such drastically different outcomes that being the better player at analyzing risk vs reward is completely nullified, i.e. coinflips.

The closest that otherwise viable options (so no Eviolite Chinchou) get to hard checking Wingull are Tirtouga and Eviolite Pursuit Pawniard. Tirtouga struggles to come in more than once after a Scald, especially if the Scald burns, and Scald into Hydro Vortex usually KOes after rocks. On top of being unable to switch into Waterium Wingull, Pawniard will often lose to Protect / Roost Flyinium Wingull. A lot of other soft checks are vulnerable to Scald burns as well, which has a 51% chance to burn over two of them.

The list of Pokemon with such limited viable checks even when prepared for is quite short, and of these, Wingull qualifies for uncompetitiveness the most.
- Abra, Gastly, and Diglett are as hard as or harder than Wingull to hard check (Diglett can't be checked at all), but they have wholly reliable counterplay in trappers. If you have a Pursuit trapper for standard Gastly/Abra variants, or Eviolite Trapinch for standard Diglett variants, they will never obtain more than one KO; the potential damage they can cause against a prepared team is capped.
- - Wingull is also much harder to revenge-kill safely with Choice Scarf users. Protect doesn't really help Abra play around Choice Scarf users the way it does for Wingull because of Wingull's far better defensive typing; for example, Magnemite can't just click Flash Cannon against Wingull, and is instead put in a potentially poor position trying to revenge-kill with Volt Switch. Gastly and Diglett can hardly run Protect at all without a huge opportunity cost (kind of awful on Gastly anyways)
- Scarf Rufflet and Darumaka arguably don't meet a base level of viability to qualify for a competitively minded team and so a suspect, even if they are able to force a comparable number of 50/50s (non-Scarf Rufflet doesn't really force these to a comparable extent). Scarf Rufflet isn't completely unviable, but the gap in viability between it and Wingull is definitely something to consider.
- Ponyta and Doduo as a whole arguably lack counterplay to the same degree as Wingull, but they are much more reliant on having the right set to be perfectly uncheckable against common threats; Wingull's highest potential threat level can be reached against almost all teams with a single set and two possible items.
- - Ponyta and Doduo rely on recoil moves (special Ponyta is easily checked), which can certainly be used to play around them. Wingull relies on an inaccurate move, which weakens its sweeping attempts comparably or even moreso, but is not a reliable means of counterplay for the opponent.
- - Ponyta needs to find an opportunity to set up Flame Charge to avoid being trapped by Diglett, which is something the opponent can take advantage of to counterplay.

Essentially, think of a Wingull suspect as an Abra one with less emphasis on outright brokenness and more on uncompetitiveness, which qualifies it for a suspect more imo.

All of the above was written with a moveset of Hurricane/Scald/Protect/Roost in mind, Flyinium being the primary option but Waterium being worth considering as well. Wingull has a few other options like U-turn, SubBJ and so on that allow it to pick and choose its counterplay further.