Riot - Why can Warwick cast skills, items, and smites while he is suppress mode yet Malzahar and Urgot can not?
Your question is making inaccurate assumptions.
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Malzahar and Urgot can, in fact, use the same item-actives and summoner spells as warwick mid-ult.
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Summoner spells and item actives are not the same thing as QWER abilities and are treated very differently.
Biggest difference is most item actives and summoner spells have no casting animation at all, won't interrupt QWER+auto-attacks, and can be cast in a wide range of circumstances.
Summoner spells that don't grant mobility can actually be cast while under any type of CC outside of silences and suppression specifically. Things like Smite, Barrier, Heal, Cleanse, Clarity, and Ignite can be cast while knocked airborne, stunned, rooted, feared, polymorphed, and more.