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The unit is fine with its stats. Compare it's performance and price against Ost T3 builds, it does alright. But there is just no window or role in which you'd really want to buy one. If we assume the SU76 is decently priced for its performance but is not bought because of other reasons (timing, niche, factional reasons etc), buffing it is highly risky and could make spam strategies meta again.
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Exactly.
This is the direct result of the "rush to end tier" mentality and the call-in changes. Certain unit are simply not worth investing in due to advantages of going T4.