In my opinion, too much crystal and black/dark malt. When a recipe looks impressive it doesn't necessarily make impressive beer.
As some of the brewers mentioned pH will be low due to crystal and dark malt being inherently acidic.
Maybe keep the specialty malt to the side and steep it, I'd boil it a little bit. Cool it, test pH, and add the liquid into the base mash until desired pH is hit. The inherent pH of ale malt reduces pH of RO water to usually 5.7/5.8 right off the bat. Maybe if pH is a little high add some of the dark mash to reduce pH before sparge.
"Mash at 162 for 30 minutes and plan your OG accordingly. This will create more long chain sugars so even with a high FG it won’t be as sweet."
Alpha doesn't work quite that way on starch. During a rest at 162F Alpha releases more sweet tasting, nonfermenting, sugar than glucose. When a high mash temperature of 162F is used, it's used at the end and when two lower mash temperatures are used, first. The length of the rest varies, it's based on the lengths of the other two rests which are based on the style/type of beer. It has to do with balance.
During primary fermentation yeast rips through glucose, cranking up ABV and leaves complex sugar, dextrin, and sweet, nonfermenting sugar behind.
The lower the mash temperature during saccharification, more glucose is released. Moonshiners rest mash at 150F because Alpha cranks out more glucose than sweet, nonfermenting sugar.
When amylo-pectin is in solution Alpha release A and B limit dextrin which are types of sugar responsible for body and mouthfeel. The types of sugar are tasteless and nonfermenting. The starch makes up the tips of grain, because it's complex starch it's the richest starch. Take a look in spent mash and you'll notice a bunch of small, white particles, it's amylo-pectin. It's left in spent mash because temperatures used during infusion brewing aren't high enough to allow the starch to enter into solution before Alpha denatures.
At 162F Beta is wiped out. When Beta is wiped out conversion won't occur. When conversion doesn't occur, maltose and malto-triose, complex types of sugar that are needed to make ale and lager, don't form. When the sugar doesn't form secondary fermentation isn't required and the beer needs to be primed with sugar or injected with CO2 for carbonation.
Alpha is responsible for: Liquefaction (amylose starch chain is cut), saccharification (sweet tasting, nonfermenting sugar and glucose are released when the chain is cut), dextrinization (A and B limit dextrin are released from amylo-pectin).
Beta is responsible for conversion. During conversion Beta converts simple sugar, glucose, released by Alpha into complex sugar, maltose and malto-triose. Conversion has nothing to do with starch.
When a recipe recommends high modified malt, single infusion, only primary fermentation and adding sugar or CO2 for carbonation, the beer will be similar in quality to Prohibition style beer.
I believe there are three or four companies producing Marris Otter, one is producing low protein malt. Go on line and find the spec sheets for the malt and use the malt with the lowest percentage of protein. The company is producing 8% protein Marris Otter. The less protein, the more sugar. The pH, level of modification (Kolbach), color, extract efficiency, gravity per pound, saccharification time, are a few numbers listed on a spec sheet. Every sack of malt comes with one because malt is inconsistent.
