Imperial plasma weapons usually only overheat when used too often or overcharged. Normal use of their lower settings doesn't usually cause explosions or excess coolant venting into your face. The Imperium just generally prefers damage over safety and orders their forces to use the guns on their higher settings, because guardsmen are cheap and plasma is usually used on high value targets like Meganobs or Chaos Terminators, so you need to make your shots count even if it risks the operator.
I don't think the Imperium in this case is prioritizing safety over damage, because although the guardsman holding the cannon is expendable, the cannon itself is not. Just a case of the Imperium's tech breaking down and having to make do with unreliable machine spirits and explosions
So, question for those more familiar with exact official detail of lore, particularly Imperial Lore. Tau have lots of mass-produced high-scale equipment, better than standard Imperial Issue, though their prototype equipment usually isn't as good as Imperial Archeotech (saying Pulse Rifles are the Tau's most advanced equipment is like saying a hotshot lasgun is the Imperium's; rail rifles are fucking great, brah, even if they don't have fancier ways of killing their target than 'very large holes in body'). Is the reason the Tau are able to manufacture their quality gear in such quantities that they still have an understanding of science throughout their general population and knowledge isn't kept in hyper-vaults unless the Ethereals decree it? You can say that they don't have to equip as much, but an entire caste of their population is Fire Caste, and they almost all become military personnel, and they have neither forge worlds nor hive worlds with which to enact the whole 'megaproduction' thing.
They don't have to equip as much, the entire Tau species is insignificant when compared to the logistical horror that is supplying the galactic plague of humankind. If you replace the lasgun, there is no way in hell you can standardize that without losing what could potentially be a noticeable number of guardsman and ammunition. Lasguns may be shit, but no matter what side of the galaxy you're on they are the ak47 of the milky way, there are plenty of spare bits and ammo to spare
Certain worlds, particularly mechanicus ones, are hyper-empirical even in the face of the reality-bending warp. But they're also usually ran by the mechanicus who either hoarde the good stuff or will turn you into a servitor for profaning machine spirits or embracing techno-heresy. That the Tau have no restrictions on AI or forbidden knowledge from their lack of MOI uprising or chaos viruses in their datalinks also helps things. Their scientists are also not completely insane, which helps I guess
Also incentive-wise, the Imperium has everything it needs to survive, with older-tech being the best shit ever. Rarely does anything new justify its cost compared to searching for something already made in the Imperium, whereas for the Tau necessity compels them to innovate or go extinct. I think the AI component is very very significant, just running off of lore from the last chancers series, particularly where they have one Imperial criminal whose crime was he "improved" Mechanicus tech and explored xeno-tech, relevantly, explored Tau xeno-tech. Ultimately gets electrocuted after trying to steal a tau battlesuit and the battlesuit recognizing he was a hostile, the Imperium is looking for reliability and replaceability over massed ranks of elite shock troopers (which are largely made obsolete by spehss mahrin anyways), or trying out new tech which could backfire spectacularly. Lasgun never backfires. Attrition warfare is their strength, if 40k was only attrition warfare the milky way would be more tank and guardsman than there are atoms in the universe