If you don't have 100% confidence in parrying the next heavy attack, just do a normal blocking and back down to catch up the tempo, don't risk taking full damage, or you'll drive your medic mad. The Scrake is a maniac wearing a butchers outfit and has a chainsaw attached to his left arm. Most melee weapons can use reload button to cancel the blocking recovery animation, which can decrease the time you need to begin the next parrying animation. Same applies to FP, unless you absolutely need to solo it with Pulverizer or hold it off, just take a single hit to derage it and get away immediately so your teammates can get another shot at it. To prove otherwise show a video where you would play a vanilla HoE game sharing a lane with mates AND 1) you manage to have ReU stack enough to 1 shot a scrake in high enough share of cases (id say 80+ would warrant running Railgun instead of M99) 2) theres no detriment to the gameplay otherwise (e.g. You should also take action accordingly, don't face hugging every single zed you see, especially when your sharp/demo needs only one headshot to kill SC, they can't get a clear shot if you send the SC into various of unpredictable animations. The only logical step would be a scrake boss, if not the matriarch. So a common tanking tactic is to activate red eye by parrying, then switch to Bone Crusher blocking for maximum damage mitigation. The red eye buff gives you 40% extra all-damage resistance, which can be combined with other resistance.
Most weapons block more damage when parrying than simply blocking, except Bone Crusher, which does the exact opposite.
